G-Max Rapid Flow hits the target for full damage even if it is protected by a protection move, including Max Guard. Its power and whether it is a special or physical move depends on the move it is based on.
Except in certain circumstances, successful hits with this attack become critical hits. Ignores passive skills that would reduce the damage of this attack. Ignores passive skills that would protect the target against a critical hit. Ignores the target's Damage Guard Next effect.
This article is part of Project Moves and Abilities, a Bulbapedia project that aims to write comprehensive articles on two related aspects of the Pokémon games.