Merciless

 is a Pokémon ability introduced in the seventh generation. This ability critically hits poisoned foes. It is the signature ability of Mareanie and Toxapex.

Description
Pokémon with this ability will always critically hit poisoned targets excluding when the target Pokémon is immune to critical hits either through an ability like Battle Armor or under the effects of Lucky Chant.

Pokémon with Ability

 * Mareanie
 * Toxapex