Defense and resistance
What is the difference between defense and resistance? Why some units have good defenses, while others have good resistances? For example, in Knalgan Alliance, dwarves have good defenses in mountains, but they cannot defend well in forests. Outlaws are very vulnerable, but it is very hard to hit them.
Defense in Battle for Wesnoth means, that any unit in game have a chance to dodge the attack. In simple words, unit with better defense is more lucky and only a few hits will hit them. Unit have different defenses on different terrains.
Rebels have access to this Elvish Rangers. They have a lot of experience in surviving in the woods, hills etc. So, this ranger is covering very well in these terrains and there is a very small chance, that someone with sword or bow and arrow will hit this unit. On flat plains, this unit does not have anything, that will help with defense. Defense here is 40%, so from 10 hits, probably 6 will harm this unit, while 4 will be safely dodged. In forest, defense is as high as 70%, so ranger can stay here for much longer time than in the flat plains.
Another unit, like this Merman Spearman, can defend hexes in a completely different way. They are generally weak in forests or hills. They even cannot reach mountains. However, when fighting in water, this unit is better than Elvish Ranger. His defense is 50% in deep water, 60% in shallow water and even 70% in coastal reef.
Resistance is all about what will happen to the unit that gets hit. So, when a unit is attacked, some hits (amount is based on defense on the terrain) will harm unit. Resistance means than sometimes a sword and a club can make different damage to a unit. Or in another words, some units have armor, that is good against spears, but nearly useless to hammers or fireballs. Similar units have similar resistances.
Dark Sorcerer have average defenses and resistances. Blade, Pierce, Impact, Fire and Cold can do the same damage. Only difference is the Arcane damage. Arcane is good against skeletons, drakes and simply to say, anything "magic". Dark Sorceror have a 20% resistance to Arcane, so succesful attack of 10 will do lower damage, only 8.
Things get much more interested with this Fire Drake. Enemy drake can use fire against this drake. Attack with force 10 will be lowered by 60%, so only 4 hitpoints will be lost. Dark Sorcerer with cold damage is more dangerous. The drake has -40% cold resistance. Attack with force 10 will harm this drake by 14 hitpoints. Here are his resistances against all 6 types of attack:
Undead skeletons, such as this revenant, have also different resistances. Killing them with swords or arrows will be very slow, but arcane and fire attack can kill them easily, or forces them to retreat. Resistances of an undead revenant:
Marksman and magic attacks
Units with Marksman are good against well defended units in good terrains. Their chance to hit is very high, at least 60%. So, hiding Elvish Ranger will be as vulnerable in the forest as in the flat plains. Marksman is activated only when attacking, not defending. Magic attacks are even more deadly. Attack have 70% chance to hit, in both offense and defense.
Elvish Ranger will have this defense:
To kill an important unit fast, read the profile of that unit. The fastest way is to attack it with your multiple units with magic attacks of the correct type. About 6 Mages would kill a powerful Revenant quickly, because their fire and arcane attack is great against skeletons. Although the skeleton might try to dodge attacks, terrain will not help him much against magic.
TIP: Units with high defenses and low hitpoints, like outlaws, are a great target for mages and other units with magic attacks.