WHOA. I replayed level 2 and a crap load Teramid Repises flooded my screen. There were so many, I gained more gold by killing them than the gold I got in replaying level 15
The whole thing is made a lot easier by being biological. Use crystalize on all enemies except for one, and then it just becomes 2 or 3 on 1, instead of 3 on 3 or 2 on 3
The Barrier Decoy is extremely useful. It's saved me from a whole lot of trouble. I say it's the most useful thing in the game aside from main turrets.