I was using a team in Pokemon Showdown, and this guy's Rhyperior goes for Max Quake. I know that Hydreaigon has levitate, so I don't expect it to work, because Max Quake is the ground-type Max Move. But it HIT. I checked Rhyperior's possible abilities and the data for the move on this particular website. Nothing says that it should be able to hit. So, why did it hit?
There is only one possibility I can think of
Let me explain, Galarinian wheezing has the ability "neutralizing gas" which disables all abilities on the field, so Max quake could have hit.
that is an example of me hitting a heidreigon with Max quake
Your hydreigon was grounded , meaning it can be hit by ground type moves. It was probably hit by something like Smack down which negates it’s levitate ability. Either that or a Pokémon had previously used gravity, or you had used roost.