A new Mega Evolution of Victreebel has been revealed in a new trailer. The video takes the form of found footage
with two people exploring an old spooky house. At the end a third trainer is trying to control their Victreebel which has Mega-Evolved.
Official description: The volume of this Pokémon’s acid has increased due to Mega Evolution, filling its mouth. If it’s not careful, the acid will overflow and spill out.