A torrent of water appears that Squirtle "surfs" on top of. The attack does multiple hits with minor knockback towards the end. It is difficult to interrupt as a recovery move, as the hitbox is large, disjointed, and directly in front of Squirtle. The movement direction of the attack can be slightly altered with the control stick to be more vertical or more horizontal.
Waterfall was introduced in Generation I and was formerly a signature move of the Goldeen evolution line. Starting in Generation II, Waterfall is an HM (Hidden Machine) that allows a Pokémon to learn the move, which, when used outside of battle, allows the player to go up and down waterfalls. Prior to Generation V, Waterfall was HM07 and HM05 in Generation V and VI. In Generation VII, moves are no longer used outside of battles and HMs were removed as a feature. Waterfall, along with some other former HMs, became TMs instead. As such, Waterfall is TM98 in Generation VII. In battle, it is a physical Water-type attack since Generation IV that has above-average power.