Get this tower (dont remember the name of it) http://imgur.com/IWO2nJt , miss it so much , You can use the hero IO wisp spirits for it
Other Suggestions: I want towers that need some type of strategic mind behind it, towers that cant be placed like everywhere for example:
Hook tower: Hit all enemies the hook passes trough in a straight line, notice: can only be casted in 4 directions: up down left right..( you can choose activate within the tower in what direction)
The hook will be casted with a massive dmg straight forward fast but upon return the hook is getting back twice as slow the speed is reduced. (so the tower is kinda slow but if u place it well u can hit alot of units)