Psywave is a Psychic-Type move in which an unusual psychic wave is used to attack the user's target, a move that varies in intensity.
The random amount of damage inflicted by Psywave is a result of Random Number Generation, or RNG for short. The randomly generated number can vary from 0 to 10, fitting into the how the move's damage is calculated like so, with the damage being rounded down:
(X + 5) * (Y / 10)
X is the randomly generated number, while Y is the User's Level.
Pokémon that Learn this Move via Level-Up
Pokémon that Learn this Move via Breeding