Well, in my opinion, you could add some living creature into the lava if you aren't thinking of doing that already, maybe some weird looking fish jumping up from the lava from time to time, and maybe it is able to attack you for very little damage if you are very close to the lava, something like a piranha that lives in lava instead of water. A constant earthquake that shakes the screen up and several rocks falling down seems to be good for me, but this might be available only in harder mode as the screen shakes up, it is harder to control your character.
You could add some plant growing on some of the rocks or cliff, or probably even on the lava as well. Another one that I think of is that you could design some of the rocks or cliff into something like an evil laughing face, since this stage is on Chapter 6, Kar'Gath right? Which is a place of evil, instead of making them just a normal rock or cliff.