I know I am fairly new and I do not know a lot about this game, but I just played a comp and tried it out for myself and it seems great. I thought I would share.
Forest Troll / Sea Troll / Kraken / Queen Mab
My team level is only 6630 and I just beat a 9000+ team with the comp. It is just an infinite loop. Forrest Troll tangles the first unit, so they can't skull attack and Queen freezes everyone else so they cant loop. It was pretty fun and thought I would share!