EffectWML
From The Battle for Wesnoth Wiki
				the [effect] tag
The tag [effect] is used to describe one modification to a unit. Any number of [effect] tags can be used to describe a complete modification. Modifications are permanent changes to a unit; currently there is no way of removing a modification.
The following keys are always recognized for [effect]:
- unit_type: only apply this effect if the affected unit's type name matches the value (can be a unit type or list of types).
 - times: describes how much time the effect is applied. The default is to apply the effect once. Other possible value : "per level" which means that the effect is applied level times, where level is the unit level.
 - apply_to: describes what the effect actually affects.
 
[effect] uses different keys depending on the value of apply_to. apply_to can take the following values:
- new_attack: will use all other keys and tags as the description of an attack that will be added to the unit. See [attack] in UnitWML.
 - remove_attacks: remove the matching attacks. All tags from the attack filter construct will be used to match the attack; see FilterWML. Do not use a [filter] tag otherwise it will not work properly.
 - attack: find an attack and modify it.  All tags from the attack filter construct will be used to match the attack; see FilterWML.  After that, the following keys and tags can be used to modify the attack.  Note: do not use a [filter] tag.  Just put the keys you want to filter on inside the [effect] tag.
- set_name: change the attack's name (ie identifier).
 - set_description: change the attack's description (ie displayed name).
 - set_type: change the attack type. The standard values are blade, pierce, impact, fire, cold, and arcane.
 - [set_specials]: change the attack's specials. The specials to add are given exactly as in the [specials] tag.
- mode: if append, adds the given specials to the attack. If replace, replaces the existing specials with the given ones. Default replace.
 
 - remove_specials: remove the listed specials. The value of this key is the coma-separated list of the id of the specials to remove. This key is always evaluated before a [set_specials] tags in the same [effect]
 - increase_damage: increases the attack's damage. This can be positive or negative, so you can use it to decrease damage as well. If it ends in a percent('%'), the change in damage will be a percentage ratio of the attack's original damage.
 - increase_attacks: increases the number of attack strikes. Like increase_damage, it can be positive or negative, or a percentage.
 - attack_weight: change the attack's attack_weight. See [attack] in UnitWML for explanations about attack_weight.
 - defense_weight: change the attack's defense_weight. See [attack] in UnitWML for explanations about defense_weight.
 
 - hitpoints: modifies the unit's HP and/or max HP.
- increase: the amount to increase the unit's HP.
 - heal_full: if present and not set to "no" the unit will be put back to full HP.
 - increase_total: will increase the total HP of the unit. Can be specified either as a negative or a positive value. It can also be specified as a percentage of the current total; i.e. "-50%" will cut max HP in half.
 - violate_maximum: it the unit ends up with more than its max HP after these modifications, and this key is present (set to any non-null value, ex. yes), the unit's HP won't be lowered to its max HP.
 
 - movement: modifies the unit's movement points.
- increase: maximum movement is increased by this amount. It can be positive, negative, or specified as a percentage.
 - set: maximum movement is set to a specific value.
 
 - max_experience: affects the amount of XP the unit needs for the next level.
- increase: how to change the xp; again it can be negative, positive or a percentage.
 
 - loyal: no keys associated. The affected unit will be loyal i.e have an upkeep of 0.
 - movement_costs: speed through specific terrain is modified
- replace: If set to "true", any new values replace the old ones. Otherwise, new values are added to old values (negative values allowed).
 - [movement_costs]: a subtag that describes the new movement costs just like in UnitWML for describing a unit type
 
 - defense: Sets unit chance to be hit in specific terrain (100 - defense value)
- replace: If set to "true", any new values replace the old ones. Otherwise, new values are added to old values (negative values allowed).
 - [defense]: a subtag that describes the new defense just like in UnitWML for describing a unit type
 
 - resistance: Sets percent damage taken from combat
- replace: If set to "true", any new values replace the old ones. Otherwise, new values are added to old values (negative values allowed).
 - [resistance]: a subtag that describes the new resistance just like in UnitWML for describing a unit type
 
 - variation: switches the unit into one of its variations.
- name: the id of the variation to invoke.
 
 - type: transforms the unit into a new unit_type. Template:DevFeature
- name: the id of the unit_type to invoke.
 
 - status: modifies the status affecting the unit.
- add: a list of status modifications to add. Beware, these may be reapplied later, such as when the unit is recalled or levels up; if in an event, you can use [store_unit] and [unstore_unit], modifying unit.status.name directly, to avoid this, or if you are creating the unit, you can just add it to the unit's [status] tag in the [unit] tag. These are listed in [status], SingleUnitWML.
 - remove: a list of status modifications to remove.
 
 - zoc: toggle the zone of control.
- value: new value for zoc (0=disable, other=enable).
 
 - profile: customize the profile for this unit type
- portrait: new image to display when the unit speaks
 - description: sets the text to display when hovering over the unit's type in the righthand pane
 
 - new_ability: Adds one or more abilities to a unit.
- [abilities]: A subtag that contains the ability definitions.
 
 - remove_ability: Removes one or more abilities from a unit. Abilities are not reference counted: added, added, removed = gone.
- [abilities]: A subtag that contains the ability definitions. Strictly speaking, all that is needed is the id= inside some tag.
 
 - new_animation: contain animations that will be added to the unit
 - image_mod: modify the image path function(ImagePathFunctionWML) of all the unit's frames
- replace: the image path function to be used, e.g. "RC(magenta>red)"