Writing out of a corner

My brother always tells me that when I write my MC into a corner all that is needed is guns, ninjas or zombies. I'm not sure I agree with the three methods, but it is true - sort of. One way to get out of a corner is to create an action that forces the character to move, to do something that will power the plot along.

I'm always getting into trouble where my character has too much reign over the plot that they end up in some situation or circumstance that I can't see any way out of (yeah, one of my MC's in a story I've benched at the moment decided they wanted to act all crazy and dangerous that they got put in a padded cell... now that's a corner. I think I'll just chuck a ghost into the cell with her, which does work since it's a ghost story).

That's not the only corners a writer can encounter. What about needed to defeat a foe when the hero is so at a disadvantage that there's no way out. This is where I'm at with my current WIP. My MC (after sneaking out of the house) goes to a club and is attacked by a water nymph who's actually made of water. What's the worst place to get trapped with this sort of creature? Yep, a bathroom... so, now I have to figure out how to kill a creature made of water in a room of water, and she's only got a lighter, a can of mace and a pocket knife.

Wow, that sounds like a case for Magyver. Oh well, whatever the solution is, it's going to be messy.

So, how do you write your characters out of corners? Have any of you found your characters up against villains that have no obvious weaknesses? Any suggestions on how to kill a creature of water?