With skill changing method, you can mimic any A.monster and multiply their ability (Healing Fairy, Endless Heat...), you can put some powerful passive in the back while having actives skill in the front (Immortal Charge, Primordial Remedy...)
There are also some good hero skill you can use (minigun-gunner, poison fog-gardener, flame fist....), but be careful when using hero skill (Goddess Advent - don't work on monster)
I also found that (Higher One, Immortal One - (maybe) don't work on normal monster), but haven't tested the (Power of Darkness, Power of Nature...)