2nd big project - help!

So this is a little mini fantasy game where you, Halo Silverfilter, needs to fight all the bad guys and defeat Lichen Zenspider at the end. However, I've been having some difficulty. We're up to Chapter 5 (I think) in the Alice textbook in class, so we can make all the requirements for the project, but I think extra, higher-level stuff is going to be need to avoid screw-ups. (Plus, the better = more bonus points.)

Here's my world, and here's my current predicament:
How can I get the player to click on an enemy, (or somehow target it = 1. Fire, 2. Frost, 3. Arcane - the whichEnemy would be the closest?) and have her shoot it with one of the three magics I have given her? (Frost, Fire, Arcane) I thought maybe three different buttons with two parameters "whichEnemy" and "whichMagic", but when I stick it in there, it'd be pre-programmed to "kill" a certain one, instead of the one the player wants. I'm not quite sure what to do. If anyone has any suggestions, I'd be very thankful!

Anyone have any ideas? *bump* Btw, I'm NOT asking for you to finish it. Just for a few ideas on how to get a "targeting" system.