First lets look at the cause for each of the abilities, Mega Evolution occurs when certain pokemon are exposed to evolution stones that have been irradiated by the aura of the legendary pokemons Xerneas and Yveltal. When a pokemon dynamaxes, it has a significant increase in stature and access to special G-Max moves( which behave similarly to Z-Moves) while certain pokemon have the ability to 'Gigantamax' which gives them a completely new look( like in mega evolution) and Max Moves and/ signature G-Max moves( once again like signature Z-Moves of certain species).
