ill give a little guide.
ill tell you what skills you need. a lvl 20 should be able to do it. You need high armor, initial mana, and anything else including mana except mana over time put extra points into but not to much. Keep some on pre gems (just enough for two)
Build level 4 gems and keep two level 5 for when he comes out try to clear out the two tough waves before hand if they get to the end theyll distract your towers from the weirdo that i just killed today (lol i found a way on my 5th try) Well when you start put your gems in orange in front then armor deplete then finally everything else. Well put two things into manapool get it up to 3710 when its there you should be able to banish him once back to the start. put up about 8 trenches from the start to the end of your towers. Build 10 tops 8 bottom towers from the start on. Then have two beside eachother with a trench to slow him down. Do not put on fast-play while hes out. When hes gone through it once and coming back the second time everytime hes completely out of reach of one tower throw it at him. Keep blue and purple in the front when you fight him. If you leak any armor should keep it at a small penalty but its still a penalty of mana all the less. Do not presend him or the two waves before him if you do you will die and be pounded again and again. If you follow this once or twice figuring out where you need to place towers for the highest efectiveness You will win.
Once hes out of the tower clump for the second time you should keep your level 5s and put them into the two towers that hes coming up on keep them far enough away so you have time to get them set up. then if your lucky you can thow them and kill him i had thrown the first one of my 5 and had my other in my hand when i saw pretty fireworks lol.
gl hf
I forget my name