バケモンが

a monster

→ バケモン
phrase Rare #38,430
a monster バケモン is a colloquial form of 化け物 (monster); が marks it as the subject. It may be used as an exclamation or in an incomplete sentence.
JA: 外にバケモンがいる!
EN: There’s a monster outside!

どうだバケモンが!

How do you like that, you monster!

— One Cut of the Dead (2017)

外にはバケモンがほかに方法がある!?

Are there any other ways to deal with the monsters outside?!

— One Cut of the Dead (2017)

すぐ戻るんで外にはねほらバケモンが!

I’ll be right back, so don’t go outside—look, there’s a monster!

— One Cut of the Dead (2017)

外にはねほらバケモンが!

Outside—look, there’s a monster!

— One Cut of the Dead (2017)

バケモンが!

You monster!

— One Cut of the Dead (2017)