4 new monsters were introduced in the Heroes War Returns patch. They are Martial Artist(3 star), Neostone Agent(4 star), Assassin(4 star) and Neostone Fighter(4 star). Below are their skill descriptions courtesty of Com2us. The Dark Neostone Agent is a natural 5 star.
I will be doing a review of them in the coming weeks. Looks like an interesting bunch!