Hints: for those of you who are stuck.
1 - use the KEYBOARD shortcuts!
2 - enemies have resistances to certain elements. Some (like the orange worms) are impervious to an element.
3 - recycle and replace often. Any enemy that escapes is that many fewer resources to hit the next wave with.
4 - To beat Extreme, it's useful to know that the slowing effects of certain elements stack, that is, both can be in effect at the same time.
5 - Writing reviews encourages more games to be made by me ;)