The experiment is here-- two taunt ability monsters. Was it a good idea?
I found Merdaali Guardian to be an okay addition. She did heal Leviathan after Hellondale resurrected it which resulted in that taunt monster eating more attacks.
Leviathan and Wave Brood did take a lot of damage for themselves which gave my three main magic attackers time to attack.
I think if I could include Phantom of the Abyss and Ruler of the Seas, this team might be more potent.