Answering the last valid question and the invalid ones..
What if Deviljho suddenly appeared in Gensokyo?
I never played Monster Hunter so I wouldn't know, but from what a friend told me, I'm guessing the gensokyans would freak out.
...what if Chihiro was spirited away to Gensokyo?
What Chihiro? Anyways, at least I don't really have to answer this one properly.
What if... (yay more bashing) Tojiko could magically turn her ghost tails into legs?
Ghost lovers would be a little sad. Her ghostly bottom is part of her charm. It's like a mermaid, but transparent and creepy!
What if Cirno was actually the strongest?