How do I get the TM for Secret Power, and what games is it in?
You get Secret Power on:
RSE: Route 111 (a person north of the desert I believe near a tree) and Slateport city (the giant market)
FRLG: The Cuttable Tree on Route 25 and Celadon Department Store
DPPt: The Lower west side of the grass field in Amity Square
HGGS: A patch of land that is northeast of a northwestern house located at the Lake of Rage. You can only access this when the lake is flooded.
ORAS: The same place on Route 111