How to play vs Nightmares
General strategy against Nightmares of Meloen
The Nightmares of Meloen faction is chaotic, except for the neutral Creepers and Unstable Elemental. It is composed of quite fast units with many specials or abilities. For this reason, you have to follow the day/night cycle strictly if you command a lawful faction. They can hit very hard at night but on the other hand they have several units with low resistance or low defense. This means that, depending on the units you recruited, you should be able to counter-attack with good results at favorable time of the day.
The Nightmares of Meloen don't have particularly efficient units to hold villages. Taking into account the high price of some of their units (Life Thief, Howling Darkness), you can try to win through economical dominance. When advancing and retreating, capture their villages earlier and stay on yours for longer, denying them the gold to buy their expensive units. They have some cheap units too, but depending on which faction you play, these sometimes lack the capability to efficiently hurt you.
Unhatched: as this unit will charge to inflict maximum damage, you should screen your ranged-oriented units so it can't reach them. To do so you might rely on different units according to its trait as each trait give it some resistance bonus for some damage type. Should it attack, having your units arranged so that the Unhatched can only reach your melee fighters will most likely mean heavy retaliation damage for it. Get ready to finish them off on your turn whenever possible.
Black Cat: with its magical attack and the jinx special, the Black Cat is one of the first units you may want to kill if you are not Undead. It benefits from high defense but her rather poor resistances help with killing her in a minimum of strikes when your best time of the day has come. After it has hit you, Unhatched, Life Thief or Scornful Watchers will most likely follow to inflict heavy damage.
Life Thief: Arcane melee with draining. Thanks to those pesky Ghosts, we all know that units of this kind are not easy to handle. Life Thieves will likely be seen in all match-ups save the Loyalists one. Fight them with ranged fire or arcane, slow them or run away from them. As their defense and their physical resistances are lower than the Ghost's, countering them with any range unit is good enough to deal with the extra hitpoints it steals. Even the usage of blade or pierce melee can be acceptable from good defense, if you fight on an advantageous time of day.
Scornful Watcher: its ranged attack turns arcane resistance into weakness. For this reason, it will be Loyalists worst enemy and will also be seen in numbers against Knalgans and Northerners. Slow and weak, Nightmares will have to cover it with their tanks. Your ability to win will often be measured by how well you can clear the way for attacking the watcher.
Howling Darkness: as an expensive unit without melee attack, the Howling Darkness is an ideal target when you are countering, but as it is fast and skirmisher, go for hitting the unit when you have a good chance to kill or it will slip right through your net. It will often be used to support Unhatched and Life Thieves on offense to reduce retaliation and can be a threat itself at night especially against the cold-fearing Drakes.
Unstable Elemental: this versatile unit can be used as a scout mostly in its tornado form that you can find on plain, road and castle. It will almost never fight in this form and will prefer to move to hill or forest when it is ready to fight. It's often up to you to accept the challenge or not, as it will be much slower in those forms. The Unstable Elemental's most disturbing use is when it moves behind your lines and take a defending form (quake, bramble or possibly whirlpool), cutting your retreat. The slow ranged attack of the bramble form, obviously combines well with Unhatched's charge at level 1 and berserk at level 2.
Creepers: if you are not playing a chaotic faction, this unit should not make you change your strategy. You should keep trying to catch units with more hitpoints at your best time of the day, so that you don't waste too much fire power on killing this cheap unit. If you are chaotic though, you may have to adapt in order to cope with those pests that can hit you when you are at your weakest. When attacking Creepers in melee, target the ones with fewer Creepers around so that you reduce the retaliation. When they form a chain, you can consider breaking it in two to double their upkeep.
Drakes vs Nightmares of Meloen
If both players chose random faction, Nightmares will most likely be ill-prepared for this very deadly match, but so might be you, as the saurians you'll have picked early won't be your best weapons. The Life Thief, Nightmares' best attacker, and the Drake Burner, your own nightmare killer, are both expensive and each side would wait to know their opponent before recruiting them. So if the game started at dawn, it is very likely that the first night will be quite peaceful and you will have plenty of time to equip yourself with Burners for the day.
Burners and Life Thieves are each other's nemesis' and two of one kind can kill one of the other every turn at their best time of the day. It shows how crucial the dusk will be for your Drakes, so be ready to retreat in time. As you are at least as fast as the Life Thief, if the Nightmares fall back too far at day, you will have an easy retreat. If they stay close to you to prepare a counter, retreat using Drake Fighters to cover your Burners from the Unhatched. This strategy might fail if Nightmares succeed at trapping you with Howling Darknesses. That is the reason why, using your Drake Fighters on them at day is the second objective you have to meet to keep the match going.
Depending on the number of Howling Darkness' turning to Skirmishers might be a decent alternative. Beside dealing free damage to the Howling Darkness when they are the most impetuous, the Skirmisher has additional benefits: it deals a lot of retaliation to not-slippery Unhatched, it's high defense might convince the Nightmares to get more Black Cats. On top of that, as saurians resist Life Thief's arcane, they can force Nightmares to turn to Scornful Watchers which are of not of much use against your Drakes.
Drake Burner: he is Life Thief's fiercest enemy. As you will definitely see many Life Thieves around, getting as many Burners as you can is a safe strategy. As only quick ones are truly faster than the Life Thief, when they can't reach any, they can also have a shot at the Unhatched. As both Burner's advancement are awesome against Nightmares, you should try to level one.
Drake Clasher: due to his slowness and his price, the Clasher is not the best buy against Nightmares. You can however decide to get one if Nightmares haven't got any Howling Darkness as it can retaliate the Unhatched charge with one of his two attacks depending on their trait. When Howling Darknesses are around, their mobility and their cold attack will be devastating to the Clasher with no chance of retaliation. You don't want them to get such easy kills.
Drake Fighter: the Drake Fighter is necessary for covering Burners' retreat at the end of the day as they will deal high retaliation to Unhatched's charge and they are relatively cheap. They should not however try to shield off the Life Thief as they won't be able to survive the whole night. When attacking, the Drake Fighter should focus on the Howling Darkness, the Black Cat or the Unstable Elemental, but don't forget his fire range can cheaply harass the opponent's Life Thieves if you have no better target.
Drake Glider: faster than the Drake Fighter with better defense and an impact damage type that can scare away the Unhatched, the Drake Glider can be used for holding off the Nightmares when Burners are retreating. During attack at day time, they will be useful mostly for trapping the Nightmares at dawn and preventing them from fleeing too easily. As they are not as efficient as the Drake Fighter at dealing damage to the Howling Darkness the role they can play is still secondary and you should not recruit too many of them.
Saurian Augur: the Augur with his low hitpoints and cold damage doesn't play a big role in this match-up. He will have trouble getting away from the Unhatched and Drakes won't have really time to protect him. Because the damages dealt are so heavy, his healing skill becomes less practical. His cold ranged attack should be used on Unhatched or anything else he can kill. You may take your chance and feed him with kills as the level 2 Soothsayer will be able to cure Black Cat's jinx.
Saurian Skirmisher: Depending on the number of Howling Darkness', the Skirmisher might be a good choice for recruitment. He's nearly as fast as them, doing free damage on melee, and beats them in price. However, due to Saurians' weakness to both cold and impact, keeping them alive might be a difficult task. Hence getting him is only advisable if there's enough Howling Darknesses' to guarantee a target before the Skirmisher dies.
Knalgan vs Nightmares of Meloen
When you get the Knalgan Alliance against Nightmares, you will be in control of the game. Just getting Dwarvish Fighters or Footpads will already be a test of your opponent's skill at playing Nightmares. He will have to combine a very efficient use of his units and some well-thought gamble with Unhatched to stay in the game. If you add some Dwarvish Thunderers and a Dwarvish Ulfserker, even the most seasoned Nightmares' players will have a hard time.
Dwarvish Fighter: with their dual blade/impact damage type, the Dwarvish Fighters are the purest anti-Unhatched units in the game, so get enough of them to control the Unhatched. When the time has come for you to attack, they will naturally excel at taking down anything around. Make sure you keep them on good defense however. Even when they have been cursed, they are still probably better off sitting on their favorite terrain with defense lowered to around 50% than running over 30% defense terrain for cover. Hitting back the Black Cat that just cursed them is often the best they can do.
Dwarvish Guardsman: slow, expensive and with low damage, you can't make enough use of his pierce attack to recruit any of them. As the Dwarvish Fighter makes such a good job at countering the Unhatched, you won't need the Dwarvish Guardsman's steadfast either.
Dwarvish Thunderer: with his ranged attack, good resistances and good hitpoints, the Dwarvish Thunderer is a good recruit. He will be useful mainly for staying in control at night when the Nightmares are pushing. Remaining on a mountain, he can stand well against the Unhatched and has a chance to deal massive retaliation to Black Cats or Scornful Watchers. His main offensive role will be to aim at the Life Thieves, which, if numerous enough, will make the Dwarvish Thunderers a necessity.
Dwarvish Ulfserker: with his guaranteed safe kills on the Howling Darkness and great chances of instantly killing Black Cats or Scornful Watchers, the Ulfserker is obviously a good unit to get. His biggest drawback is he can be drained to death by the Life Thief. In some circumstances the Unhatched can also kill him, so always make sure you can cover him properly before attacking. If there are some Creepers around, remember that a group of four or five (depending on ulf's traits) has a good chance to kill a full-health Ulfserker.
Footpad: with their two impact attacks they are a very convenient units to have against Nightmares. The Footpad can inflict free hits to the Unhatched with the ranged attack (has a good chance of hitting as the Unhatched's defense is below 50% nearly everywhere), while his/her excellent defense, good hitpoints and impact melee makes it difficult for the Unhatched to deal with him/her when pushing in.
Gryphon Rider: while the Gryphon Rider is an awesome offensive unit, it might have a hard time when fighting Nightmares. He can easily be trapped by the Unstable Elemental or the Howling Darkness, which could hurt him a lot due to the impact weakness. Even though he dishes out tremendous retaliation to Unhatched's charge, if the Unhatched's trait give it a boost to blade resistance (lowering each hit's damage by 5), it will never think twice before charging him taking into account their difference in price (except on daytime). Be prudent when using the Gryphon Rider. While most of the time, he only needs two hits to kill a Black Cat, putting too much hope into getting two hits against a 60+ defense unit might be a bad gamble with Gryphon Rider's 24 gold.
Poacher: the Poacher can give your recruitment a different flavor. Best defense on forest, he can exploit this common terrain that Dwarves will avoid. He can supply some hits on the Life thief or retaliation against Black Cats and Scornful Watchers for cheap price. When the Unhatched get more frequent, the Footpad is a better recruit though, since the Poacher is such a juicy target for them.
Thief: the Thief's best use is to hit Nightmares when they put themselves on bad defense, not taking much damage in the process. If the Thief can dart around and backstab anything, s/he will probably also make enough damage to prove a good investment. If a Thief gets a kill, s/he won't need much more XP to level, so you might try to feed him some. Thieves have low hitpoints, bad resistance to nearly all of Nightmares' damage and you can't reasonably hope to backstab with several, so there's no need to get too many. A strategy based on Thieves would be quite risky, as they are very quick to fall when attacked by a Black Cat & Unhatched force.
Loyalists vs Nightmares of Meloen
When Loyalists' player realizes he faces Nightmares of Meloen, his attention should constantly be focused on the Scornful Watcher. The large range of Loyalists' melee units can be used to bring them down before night. As your opponent will try his best as zocing you out from getting at his Watchers, recruiting a bit of any melee units is one important step to ruin his strategy.
While the Spearman gets the best damage per gold, he is quite easily controlled by the Unhatched. Hence you should have some Cavalrymen to attack from the distance, moreover his good impact resistance can make him a good blocker against the Unhatched.
When attacking Unhatched with Mages you should try to finish from fear that Nightmares sacrifice him on your Mage hoping for a kill. For most others attack combo, the most important is to deal maximum damage. As the Nightmares don't really have an efficient village holder, they will have to give up villages reducing their ability to heal. The only exception is the Scornful Watcher as he is so deadly that you want to have him dead.
Bowman: the Bowman is less efficient at dealing damage to Nightmares than the Mage. For this reason you should restrain yourself from getting them. However, if you lack gold or if you already have one, it can be quite useful poking safely the Life Thief and the Unhatched or against the Scornful Watcher at retaliating. His additional hitpoints can be a life saver.
Cavalryman: this is a key unit for this matchup. His high resistance to impact damage helps containing the Nightmares push at night while his speed allows him to switch quickly to the attack mode on Scornful Watchers. The Cavalryman can also successfully chase down a fleeing Howling Darkness and you can use his 3 strikes to ensure a hit on the Black Cat. His blade damage is also doing well against the bramble form of the Unstable Elemental. So get some of them and try to level one.
Fencer: get them if wounded Howling Darknesses and Scornful Watchers keep escaping your grip. They will only have small use in defense, as the combination of Black Cat's jinx attack and their own bad resistance are promises of short life when facing the Unhatched. If you have no problem killing your quota of Scornful Watchers you probably better keep the gold for a Mage.
Heavy Infantry: do only recruit them when Nightmares abuse of Unhatcheds. As soon as they appear, they will be the target of Scornful Watchers to clear the way for the Unhatcheds. As your Heavy Infantry's armor is no use against them, you should make sure they are in Scornful Watcher's range only at the second night otherwise you will probably lose too much gold. Due to their slowness, they will only be useful in defense so the best time to get recruit them is usually at dusk or first night. On attack they should target anything but the Life Thief whenever possible.
Horseman: while the Horseman powerful charge let's you hope of huge damage, its cost is a deterrent to having one in the early game. If the game gets longer and you succeed in cashing enough gold, you can then get one as he will do well at Scornful Watcher assassination with his impact resistance cutting down the retaliation, and will simply be deadly against the Howling Darknesses.
Mage: the Mage will be a powerful weapon against the Unhatched. However, his low hitpoints require you to protect them at any time of the day. Hit the Unhatched you have the best chance to kill, as even wounded his charge attack is danger for your Mage's life. Because he is so weak against the Unhatched, don't feed him with kills. He will probably never live long enough to level.
Merman Fighter: when water is present in the map, getting a Merman Fighter or two is a good idea. Since Nightmares don't have good movement on water, they can force the Unstable Elemental to move to water to control them or they will be able to reach the Scornful Watchers. When facing a whirlpool form of the Unstable Elemental do not fear to engage in combat as they have worst resistance than your Merman Fighters.
Spearman: as always, the Spearman will be the first recruit to turn to. He can both retaliate hard on the Unhatched's charges and do severe damage to the Scornful Watcher. His low price allows you to get enough to protect efficiently your Mages from the threat of Unhatcheds. Combining with Cavalryman is a must though, as you want to diversify your damage type to leverage on the resistance bonus of the Unhatched's trait and get more speed to chase Nightmares down when the day comes.
Undead vs Nightmares of Meloen
Having to fight Nightmares is one to the toughest experience for Undead. Unlike what they are used to, Undead in this matchup will play by counter-attack as the ability of make the most damages is not on their side. While you will be relatively safe on the ranged front, the Unhatched's impact will break your Skeletons in piece, the Life Thief's arcane will tear them apart while the cheap Creepers' banding is an additional threat to your Dark Adepts. So you will have to turn on the survival mode as soon as possible, recruiting Ghoul, Ghost, Walking Corpse, still some Skeletons and Dark Adept for the counter.
Always keep a decent amount of Dark Adepts on the board in order to keep Nightmares under pressure of a possible attack and the threat of a hard counter-strike. This way you will be ruling on the ranged as they will rule on the melee part. As you will unlikely face the threat of Life Thieves in the beginning, you will have to deal with Unhatched first by recruiting Walking Corpses to contain them and keeping your Skeletons on high defense. While your Walking Corpses begin taming the Unhatched, Nightmares will send more Life Thieves. Try to make them attack your Skeletons as if they get wounded, they will become an easy job for your Dark Adepts.
It is quite sure that at a certain moment, as your Walking Corpses starts getting annoying, Nightmares will recruit Creepers. As level 0 units, they are quite a natural opposition for the Walking Corpses, however they require some special techniques to deal with them. Creepers have a neutral alignment so you better fight them at night as two hits will be enough to kill them (they won't get plagued). Because the banding ability can make them inflict high damage you should always try to attack the most isolated ones, if you really need to kill one in the pack, better use the Skeleton as he resists strongly their pierce.
Dark Adept: again, the Dark Adept will be your best unit for attacking. The threat of the Unhatched's charge will be the major challenge, as three hits are enough to kill an adept at night. When they are in position to attack they should hit the Unhatched first as they will do maximum damage against them. The second best choice being the Life Thief. Try to pick your target so your Dark Adept can take the shoot from good defense or make sure you can cover him immediately. You'll want to go for a kill each time you attempt to damage an Unhatched, because even a badly hurt one will safely charge your Dark Adept for massive damage before dying.
Ghost: with drains on its arcane melee, the Ghost can enjoy this matchup. It is simply unattackable by the Unhatched without very heavy risk, and efficient enough to deal damages to the aberrations and Unstable Elementaland to a lesser extend to the Creepers. Its only problem will be when facing full health Life Thieves or Scornful Watchers. As the Ghost has worst resistance, less hitpoints and doesn't hit as hard, it should not engage in direct fight with them. Hopefully it can rely on its better movement points to make sure to keep far enough, as long as it doesn't get slowed by the bramble form of the Unstable Elemental.
Ghoul: don't underestimate the Ghoul role in this matchup. It is a decent candidate for holding village against Unhatcheds with its poison retaliation, and Life Thieves with its relative resistance to arcane. He can also poison Unstable Elemental to force them to heal, depriving Nightmares of support units.
Skeleton: it is a good support unit against Nightmares. As it certainly fears the Unhatched's impact and Life Thief's arcane melee, he can cause enough damage to make its sacrifice worthwhile. While the Skeleton can help clearing Creepers out of the way, it is not worth putting it on bad defense terrain for that as the Nightmares' counter will hurt him badly. It is also the best damage dealer against Black Cat and Scornful Watcher if they are present on the field. But it is not worth to feed it with kills, better use a Walking Corpse to plague them, or try to upgrade a Ghost.
Skeleton Archer: do not recruit any Archer, they are made of the kind of bones Unhatched likes to play with. At any time of the day, the Unhatched will be attracted by them and his impact charge attack will destroy them within the second. There is no way the Skeleton Archer can make enough damage before dying to repay its gold.
Vampire Bat: even the hax power of the Bat is not enough to save them against the charge of an Unhatched. Any bat is killed in two hits and the intelligent ones are dead in one single hit at night. If you got one, use it to steal village or disrupt Nightmares' organization. But stay away from Unhatcheds and Scornful Watchers at all time.
Walking Corpse: the use of Walking Corpse is mainly for obstructing, screening off Dark Adepts and Skeletons from their foes. You can also place them around units that are holding a position to reduce the number of spots available for attack. On attack, they should focus on Creepers and Unhatched.
Rebels vs Nightmares of Meloen
When Rebels realize they are playing against Nightmares, their first idea will be to get some Woses. While this is a good idea, the best is too wait for dawn or second night to get one, so that Nightmares are at the closest to launch the counter. When you get your Wose, you need to get some Mages quickly. They will make Life Thieves think twice before pushing at the end of the night when your Woses get engaged. At other time of the day, better to keep recruiting Elves, mostly cost efficient Elvish Fighters.
On counter, use the Wose first on Unhatched at dawn, backed by Mages, Elvish Shaman staying on good defense to slow any Unhatched or Life Thief, the Elvish Fighters covering up while other units deploy to get ready for the push. When pushing keep the Woses moving full speed while Elves try to slow, zoc in and trap Nightmares. When attacking, use Elvish Fighters on Black Cats and Scornful Watchers, Mages on Life Thieves, Elvish Shamans and Woses on Unhatched.
When retreating, have the Woses go full speed while using Elvish Fighters to cover the fleeing Mages and Elvish Shamans. As they will get wounded pretty badly keep on recruiting more to be able to hold until next day. When you can't retreat anymore, use Elves in lines, Elvish Fighters on the most exposed spots and Elvish Archers or Elvish Scouts elsewhere. Keep slowing Unhatched if your healthiest Elvish Shaman can stay on forest with some cover. On defense at night, do not use the Woses to hold the line, but rather leave them behind to regenerate as it will help make the Nightmares' Life Thieves aimless.
Elvish Archer: if the Elvish Archer does not make as much damage as the Mage and does not have has much hitpoints as the Elvish Fighter he can still be of some use. It can increase the speed of your army while making significant damage on Nightmares' melee units for free. He can replace an Elvish Scout but can't take the role of an Elvish Fighter. So recruiting one or two is enough.
Elvish Fighter: there is obviously no chance for you to win in this matchup if you don't rely on Elvish Fighter's resilience and punch. He is the guy that will bring down any ranged units of Nightmares, and he will make maximum retaliation on Unhatched or Life Thief before leaving. That is the best hitpoints that money can buy and he will act trustfully as Mage's or Elvish Shaman's bodyguard. Have a lot of them, and keep recruiting to make up for the losses you'll have in their ranks.
Elvish Scout: on wide maps, it can be good to have some, but most of time, you will get one for village grabbing only. In the middle of the game, you will go for Elvish Fighters and an Elvish Archer once in a while. You will recruit more Elvish Scouts only is you think that you have some chances to level them with the required XP being one kill lower then Elvish Archers'.
Elvish Shaman: she is as usual the hidden treasure of the Rebels. With slow special, she is able to reduce the damage Nightmares will inflict at night and nailed down the Life Thieves when they have to retreat. With her high defense on forest, she is quite difficult to take down for the Unhatcheds while they can't really get help from the Black Cat as he would feared to get slowed in front of angry Elvish Fighters. The usual things with shamans : slow the targets you can't kill, or slow a target to lower its retaliation if you intend an attack on your enemy's primary range.
Mage: the use of Rebels' Mage will be quite different from Loyalists'. As the presence of Woses will call for Life Thieves, the Mage's main role will be to put pressure on them and counter when the day comes. For this job, a quick mage is best as he can catch up with running Life Thieves. When targeting them, make sure you hit the ones with most XP as you don't want one to level. He will again be the preferred target for the Unhatched and hence should be covered with Elvish Fighters at night as the Woses will be busy running away from Life Thieves.
Merman Hunter: less useful than the Loyalists' Merman Fighter, he still can get some use if a patch of water in present in the map. Try to use them to fix an Unstable Elemental in the water. Don't hesitate to attack him as your resistances are better than his.
Wose: you can recruit some Woses as he is excellent at countering the Unhatched's charges or taking them down at day time. While he is resistant to most Nightmares' attacks, he is very weak when facing the Life Thief who can inflict heavy damage with its arcane melee while getting healed from drains. As the Wose is as expensive and slower then the Life Thieves you can't afford to let him fight them alone and should back him with Mages.
Northerners vs Nightmares of Meloen
Both factions do have tremendous melee heavy hitters: the cheap Unhatched and the cheaper Orcish Grunt. Relying on them to make a breakthrough is quite a gamble and the best way to keep in control of the game is more than often making the best use of the ranged fighters, the Scornful Watcher for one side, the Orcish Archer for the other. Due to the threat they represent, they will be the focus of the melee unit tactics.
Another similarity between these two factions is how the Black Cat and the Orcish Assassin are used. Both unit bypass the defense to hit the target and disrupt it until it has healed on a village. As both factions, don't have a healer, the villages is an important asset and should be kept at all time. Your Orcish Assassin does only impact a couple of Nightmares' units so you should keep them in low number.
Northerners make better use of terrain to improve their defense, so push Nightmares to fight you on patches of good terrain. Keep in mind to always put in front the units with more hitpoints in order to make maximum retaliation and give you the opportunity to kill on your turn. They also have more diverse damage type available and can more easily press, choosing where to attack depending on Unhatched's trait.
Goblin Spearman: evidence that the little one from the Orcish family play an essential role has still to be found. But you can still get a couple of Goblin Spearmen in some circumstances. They can be helpful at taking down the ranged oriented Black Cats and Scornful Watchers, can hold a village quite well when facing a single Unhatched and can give a hand at disinfecting an area from Creepers.
Naga Fighter: when a patch of water is available, recruiting a Naga Fighter may be required. While his range is very similar to the Unstable Elemental due to his decent movetype on land, he cannot fight as well as the Merman Fighter against them.
Orcish Archer: he is Northerners' best weapon against Life Thieves with their low defense everywhere and, for this reason, will attract Unhatched as if he was a mage. The other special of the Orcish Archer is that he will be the only unit to make equal damage to any Unhatched regardless of his trait, so you can always use him on the Unhatched that resists best the damage type you have recruited. You have to protect him though and leveling one is a big achievement for this matchup.
Orcish Assassin: the Orcish Assassin while not being able to kill much in this matchup, remains useful. You can have one on the board at any time. Aberrations and Unstable Elementals only can be poisoned, the ones that give the hardest time to Northerners can be: Unhatched, Black Cat and Scornful Watcher. Poisoning Unhatcheds is particularly efficient as they possibly get a lot of damage in retaliation if they keep attacking so Nightmares do not want them to be low on HP. When the opportunity shows, poisoning the Unstable Elemental is neat too.
Orcish Grunt: the loyal Grunt proves himself again one of the best units in this matchup. Being able to do heavy retaliation on both Unhatched and Life Thief, he is in charge of clearing Black Cats and Scornful Watchers from the map. When all the possible targets have been decimated, you can use him to protect your Orcish Archers from Unhatched or your Troll Whelp from Life Thieves. It can also be used to give the killing blow to a Life Thief, if you don't have more archers available.
Troll Whelp: he is the solution when the board starts looking like an egg incubator. His impact damage and regeneration, combined with his low price makes any Unhatched spam a complete failure. The Life Thieves like to use his arcane weakness to drain him, thus being able to hold armies of Troll Whelps, so you should only recruit them when the number of Unhatched requires them. The Troll Whelp's regeneration does not cure the effect of the Black Cat's jinx, so, if cursed, his defense will drop to a critically low level.
Wolf Rider: with his exceptional movement and his three strike attack, the Wolf Rider can have a use against Nightmares depending on your play style. He can track down wounded or poisoned units when they flee, he can also keep in range of Howling Darkness for free hitting. Generally speaking, his movetype allows you to dispatch him wherever you need one hit or two without using one of your heavy hitters.
Summary: There are two strategies to fight Nightmares with Northerners. The first one is to rely on Troll Whelps to control the Unhatched. As a consequence, Nightmares will recruit Life Thieves to heal on them while inflicting enough damage with Troll Whelp's arcane weakness and his low defense. On your side, you will recruit Orcish Archers to beat the Life Thieves down. You still have to recruit some Orcish Grunts as he is still the best unit to hold strategic places against the Life Thief. The second path you can go is to go for a maximum of Orcish Grunts. If so, be ready to see Black Cats and Scornful Watchers coming in to take at them. They will be covered by Unhatcheds that you will target with some Orcish Assassin to disrupt his organization, and still some Orcish Archers. As poison will be often used and you will face ranged units, the Wolf Rider can bring additional tactics that can help getting a kill or extend the effect of poison on a trapped unit.