vanilla edition means:

no made up abilities, at all

no huge power/pure power/tough claws/adaptability/aerialite/pixilate/refrigerate/gale wings/protean

no more than 50 points added to a single stat

no more than 20 points removed to a single stat

10 points added to the opposing attacking stat, example, mega haxorus needs +10 points to its special attack or mega chandelure needs +10 points added to its physical attack

if you want to add another type it must be explained trough its movepool, it must learn already 2 moves of the type that you want to add

example:
bellossom grass/fairy, because it gets moonblast/dazzling gleam