''There's honestly is not any hard checks for mega gyarados besides mega altaria with just dual stabs taunt/sub and ddance set.....''
Keldeo? Azu? Ferro? MZor? Tangrowth? MSaur? Mega Manectric? Those are only the A+ and A ranks btw. There are like 25 nice checks to MGyara not even considering it being pressured by rocks pre-mega and meh typing after mega