Extraordinary energy amplifies its cursing power to such an extent that it can’t help but curse its own Trainer.
– Pokémon Ultra Sun Pokédex
Wow Mega Banette’s Pokedex entry is pretty brutal, it even turns on its trainer; it looks more sinister as its insides spill out of the zippers.
It gets Prankster as its ability, but unfortunately it doesn’t get that turn one before it mega evolves.
Stat-wise, all of its stats go up a little bit after mega evolving; its Attack is increased by 50, making it a viable offensive Pokemon, though its Speed is still kind of average (it can learn a couple of priority moves).