Very nicely done. I was having second thoughts about whether making the targets invulnerable or not was a good idea, but first off, melee units can't touch the targets anyway, and second, ranged units wouldn't be able to hit them through the ice (in reality, anyway).
However, you might want to keep teleporters from being able to target the area inside the ice in some way. I know it may seem illogical in some respects, but it's like teleporting into a tree: not something you want to do, and not something very possible.
The problem is that I had to transfer this spell from my project to this map, the way I coded it in the project is kinda messy, and I did not intend to spend much time re-assemble everything (I had to concentrate on the project, and my finals you know). When I have more free time, I'll make a user friendly version.
This is a great spell!! 5\5. The only thing that makes me really sad is that I can't seem to be able to transfer it succesfully onto a map that I'm making (I can't make heads or tails of JASS), like I could with Omni-drain. You don't know how unhappy that makes me cause I'm looking for a spell just like this (. Any chance for resubmit with a little more instruction? Just wondering.