The Energon Pub

Pretty self explanatory. He's my first Transformers buy in years, all seemed fine and dandy (hey wooh, he's not perfect but its a retail Sentinel Prime figure!) but his head is stuck and I worry I'll snap Infinitus in half if I keep trying to remove the Titan Master.

WD-40

Try putting it somewhere warm for a while to expand the plastic slightly. If you're not afraid of getting it wet, dunking it in hot (not boiling) water might help.