And nothing's immune to BOTH ice AND fire. It is just a matter of learning to use the abilities right.
I was referring to the freeze effect and the brief stun from the pull at the flow stance. You can spam the burst fast enough so that nothing moves and makes you godly (assuming you can pull in the ranged units as well). As of mobs immune to both effects, Pride demon is a prime example. Sure they are not immune to fire, but they will still be attacking you and potentially kill you, since the fire burst doesn't do that much damage to kill them quickly.
But until they comes, just stand in the open and spam the burst until everything is dead. The freeze definitely lasts long enough for you to chip in the open and flow stance of the ring, and then carry on freezing stuff...