Here are my answers..

1. Nothing causes it.. er..
2. Bouncers and gun 9.
3. Any ammo can, since it's horizontal.
4. When it's iced..?
5. It makes the ring not do anything.
6. I'm guessing when she tries to get up from the springs by that hole that leads to a warp she can't get there..
7. Airboards and stuff ;P
8. Water shield or laser shield.
9. It's invisible.
10. Gun 8 and 9.
11. Hurt you.
12. Autofire gun with is infinite ;P
13. You can't kill the witch I don't think...
14. Nothing.
15. battlea

I probably got most of them wrong. ;P