I really wanna try the sets I never used. Like the earth and ice ones.
(I wonder if they'd do an earth blast set. Not sure what that would be.)
Thoughts of Marvel's Sandman come to mind. Sand is sorta like Earth, isn't it?
Or, you could just be a dirty crook. A dirty smelly crook. One who leaves behind toxic fumes, Pigpen of Peanuts fame style..
The tier 9 power could be channeling some lava from deep within the Earth (causing you to move like a Stone tank who's rooted - so not at all)
There's probably a lot of different ways to do it, but it just makes me think of Earth Control.