Ideally, you want to give this some sort of evasion, and cards like Garruks Uprising help with that
The fact is, Magic players are a very diverse bunch, and the cards mean many different things to many different people
With the Darkness type having no Pokmon to ramp Energy, its highly likely that by the time Mega Gengar EX is live, your opponent would have used almost all of their Trainers
The decks other character, Cruella De Vil, Miserable as Usual, is a much cheaper card able to be played earlier on, and can force characters off the field when shes banished by returning a character to its players hand - playing into the decks more control-like tendencies
Plus, the artwork is quite glorious, featuring a bold Pidgeot in flight against a mystical cosmic background
Rather than generating a free Water Energy each time you land on heads, this card takes one away instead