Make a target immune to a move

Principle

A Pokémon can be immune to a move for two distinct reasons:

• From the move itself: the move checks the target's conditions and decides it has no effect.
• From an external effect: an active effect on the target prevents the move from affecting it.

In both cases, immunity is signaled by returning true.

Difference with blocking (guide 002): blocking prevents the move from reaching the target and displays a message. Immunity means the move reaches the target but has no effect -- the system automatically displays the message "It doesn't affect [Pokémon]...".

From the move

Some moves can have no effect on the target based on their own rules. For example, the move Attract has no effect if both Pokémon are not of opposite genders or if the target is already under the Attract effect.

To handle this behavior, override the target_immune? method in the move's class.

Example: Attract

# Test if the target is immune
# @param user [PFM::PokemonBattler]
# @param target [PFM::PokemonBattler]
# @return [Boolean]
def target_immune?(user, target)
  return true if super
  return true unless user.gender * target.gender == 2
  return true if target.effects.has?(:attract)

  return false
end

• The call to super is mandatory to preserve default checks.
• user.gender * target.gender == 2 checks that both Pokémon are of opposite genders (male=1, female=2, so 1*2=2).
• The method returns false by default if no immunity condition is met.

From an effect

Some effects can make a Pokémon immune to certain moves. For example, the ability Bulletproof grants immunity to ballistic moves.

To handle this behavior, use the on_move_ability_immunity method in the effect's class. Despite the method name containing ability, it applies to all types of effects.

Example: Bulletproof

# Function called when we try to check if the Pokemon is immune to a move due to its effect
# @param user [PFM::PokemonBattler]
# @param target [PFM::PokemonBattler]
# @param move [Battle::Move]
# @return [Boolean] if the target is immune to the move
def on_move_ability_immunity(user, target, move)
  return false if target != @target
  return false unless move.ballistics?
  return false unless user.can_be_lowered_or_canceled?

  move.scene.visual.show_ability(target)

  return true
end

• The first lines verify that the target is the effect holder and that the move is ballistic.
• can_be_lowered_or_canceled? checks that the user's ability can be neutralized (some abilities ignore immunities).
• The ability animation is displayed with show_ability to visually indicate the immunity.

Conclusion

• Use target_immune? if the immunity depends on the move's own logic.
• Use on_move_ability_immunity if the immunity depends on an external effect active on the target.
• Return true to signal immunity -- the message is automatically displayed by the system.
• For ability-type effects, remember to display the ability animation with show_ability.