Hypnotized! By The Hypnotic Cube (2004)

Roommates Serena and Rebecca share a close bond until Serena, harboring resentment over a stolen boyfriend, acquires a mysterious "hypnotic cube" at a flea market. She uses it to manipulate Rebecca, forcing her to do embarrassing acts and implanting a deadly post-hypnotic suggestion. But the plan backfires, and Rebecca turns the tables, enacting brutal revenge. The arrival of Rebecca's psychiatrist raises questions about the cube's origins and the true nature of the roommates' twisted game.