It's a beautifully designed card, and powerful in a certain sense, though I don't really know to what extent. But I've beaten it several times with simpler cards. I don't think there's yet to be a combination that uses that card well, or I haven't found it in a good deck that combines good Leaf elements to play against this guy.

For me, there's a very good combination with this Dimensional Crisis booster, which is the following with Shadow Pokémon:

And if it has others to keep putting out Poison quickly and consistently, and by repeating the Nihilego card, it becomes a pretty lethal deck.

I love this game! What's your friend ID? Here's mine! 8184519794558385 Add me for trading. I'm sure I'll have cards you'll like.