Heal Block is a non offensive Psychic-type move.
Heal Block restricts the targets from healing in certain ways for five turns.
Affected Pokémon cannot use status moves that heal the user immediately or Wish, Lunar Dance or Healing Wish. If an affected Pokémon had already selected one of these moves to use before being affected by Heal Block, it is prevented from using the move (i.e., no PP is consumed). If a Pokémon cannot use any moves when selecting a move to use due to Heal Block (e.g., due to knowing no other moves that have PP, Choice Band, etc.), it will use Struggle.
Affected Pokémon can still use Ingrain, Present and Aqua Ring. However, affected Pokémon cannot be healed by the effects of Wish (which cannot be used while affected by Heal Block) or these moves. Affected Pokémon also cannot use the move Heal Pulse.
Affected Pokémon cannot use the move Heal Pulse.
Affected Pokémon can no longer be healed by Heal Pulse, Black Sludge, Leftovers, or a Shell Bell.
Affected Pokémon will not consume held HP-restoring Berries or Berry Juice. If an affected Pokémon consumes an HP-restoring Berry via Fling, Bug Bite or Pluck, it will not have its HP restored.
Affected Pokémon with the Ability Water Absorb or Volt Absorb will take no damage from Water- or Electric-type moves,respectively, but will not be healed by them either.
Affected Pokémon with the Ability Rain Dish, Ice Body or Poison Heal are prevented from healing during rain or hail, or when poisoned, respectively.
Heal Block will not prevent Pokémon with the Ability Regenerator from having their HP restored upon switching out.
Affected Pokémon can no longer use draining moves, except Leech Seed. Leech Seed will inflict damage to the seeded Pokémon, but will not restore HP to a Pokémon affected by Heal Block. Affected Pokémon can still use Grassy Terrain, but they cannot be healed by the effects of Grassy Terrain.
Pokémon that learn Heal Block
By leveling up
Via a prior evolution