Nice
But how it was sayed above - last red mushroom overpriced. It has 2xRange and 2xRate, but in late game it's all about gems, man.
You could made it having at least 2 gem slots, for some flexibility at such a price.
Btw, gems can be purchased right where you buy defenders ;) There is a tab right there "Defenders\Elements", so you need "Elements" tab ;P