All moves used by or against a Pokémon with this Ability cannot miss. It also allows Pokémon to be hit during the semi-invulnerable turn of Fly, Bounce, Dive, Dig, Shadow Force, Sky Drop, and Phantom Force. If a K.O.-Move is used by or against the Pokémon it will also hit.
The only attacks, that are affected by this Ability in multibattles, are likewise either used by or against the Pokémon.
Outside of battle
Outside of battle, if a Pokémon with No Guard is in the first place in the party (even if fainted), the wild Pokémon encounter rate increases by 50%.
If Wishiwashi is level 20 or higher, at the start of battle or the end of a turn, if its HP is above 25%, it will change into its School Form. At the end of the turn, if its HP is below 25%, it will change back to its Solo Form.