At the beginning, try to focus your gems on Vamps or Skully Archer (vamp recommanded since elfs will be stronger than you skully archers). Summon them in the first line and Imps or Skullys on the second. It is recommanded to stock your units on this level. If you encounter an golem on this level try to special him dead before he can do his special.
Then start building some nercos or zombies (necros recommanded since you don't have to manage the defense) to tank against those anyoing healers.
If you have problems with winning this level get some gargogyles or troll add the back and you will be fine.
One more note: If you use lich and reaps on legendary put them add the back. Don't use them as solo offensive, that way they would be killed soon after they killed the 4th healer. Ones tier 4 get released you won't have this problem anymore.