Petal Meadows Asylum was an asylum for the criminally insane. This asylum was well known for housing Kirby, a cannibalistic serial killer who was reputedly Petal Meadows' most dangerous and deranged patient. There were many other inmates as well.
Meta Knight- Kept watch over high-security prisoner Kirby, the two being old enemies.
Kirby- Plagued many nations, slaughtering and devouring countless civilians and wearing their skin for pleasure.
Squirtle- Unknown. Possibly killed many Pokemon brutally in the fighting arenas.
Mewtwo's Psychic Army (possibly)- Went insane and feral, possibly killing each other and innocents.