I like the earth/stone idea.
Possible direct attack powers:
* Earthen Fist - Blast, Indirect (from below), possibly Double Knockback
* Stone Shards - RKA
* Sand/Dust Storm - Flash
* Magma Eruption - RKA, Damage Over Time or Uncontrolled
* Sudden Pit - Blast + Tunneling UaA
* Area effect versions of all the above
Possible Control-Type Powers:
Way too many to even count - myriad forms of Entangle, Barrier, Control Environment, Darkness (sand/dust cloud), TK, even Images (make figures out of dirt, fool people using radar/spatial awareness to see through dust storms).
Movement:
Tunneling
Moving "wave" of earth for increased Running, possibly with "doesn't have to be standing / move legs" advantage. Also possibly shareable.
Possible Defense:
Shield of orbiting stone shards: ResDef, Protects Carried, RAR
Barrier + See Through Earth/Stone + Indirect
Tunneling + See Through Earth/Stone + Indirect; Ultra effective in the right conditions
Barrier with Trigger
Just be nimble as hell, confusing people who think "stone = slow"; Combat Luck, Flying Dodge, etc.