Overgrow

Overgrow is an ability in the Pokémon series that is currently used by 12 different types of Pokémon species, all of which include every single grass starter Pokémon. The ability allows the Pokémon that is using it to raise it's grass type moves by 150% if the Pokémon using it is under 30% in health points.

List of Pokémon that use Water Veil
Take note that all of the following Pokémon also have one other ability as well, making it a dual ability.