I really don't have much experience with this set, which I find a bit unfortunate because I love Ice Age and Alliances, despite the massive amount of crappy cards in Ice Age...
The first card that came to mind was actually Dark Depths. Not sure if it's because Dark Depths was the first card from the set I saw (if I remember correctly, or because it's just such an unusual and potentially powerful card. But I can't agree with Ransac again. It's unseemly. So I'll have to nominate something else...
I'm going to go with Braid of Fire. I'm not sure how I'd break it, but there are a lot of possibilities...