There are a total of 48 mega evolutions, with the only games that had introduced new Mega forms would be XY and ORAS (Omega Ruby and Alpha Sapphire). Gen 7 games had kept in the mega evolutions, but didn't introduce any new ones in favor of the newly introduced Z-Moves in Sun/Moon, while the Gen 8 games removed the Mega forms entirely as well as Z-Moves, due to how cluttered it would be having Megas, Z-Moves, and Gigantamax forms, all in one game.
