When a Pokémon with Torrent uses a Water-typemove, the move's power will be increased by 50% if the user has less than or equal to ⅓ of its maximum HP remaining.
Generations V onward
Instead of boosting Water-type moves' power, Torrent now technically boosts the Pokémon's Attack or Special Attack by 50% during damage calculation if a Water-type move is being used, resulting in effectively the same effect.
In Pokémon UNITE, Torrent is Blastoise's and Greninja's Ability that activates when the user is at half or less HP. Blastoise's increases Attack and Sp. Attack by 20%, while Greninja's increases Attack by 5% and movement speed by 12%.
When Empoleon becomes weak or tired, its body becomes surrounded by a light blue aura for a few moments. Then, its eyes flash light blue as well. Empoleon's Water-type moves then get powered up.