In Pokemon Go, the Mega Evolution system is governed by a resource called Mega Energy which players have to collect in order to Mega Evolve their Pokemon like Charizard, Venusaur, Blastoise, Gengar, ...
On top of the above raids, a Mega Raid Day is usually scheduled monthly to reveal a new Mega Pokémon, but there is no guarantee one will always show up as Niantic slowly runs out of new Megas to ...