My mood presently says Titans Return Alpha Trion, for his robot mode in particular. This character is supposed to be a wise, kind, scholarly figure, but in this toy he looks like some kind of undead warlock-cum-knight returned from his tomb to take back his dominions, and that's a monster even if it's not (currently) a beast.

I have difficulty looking at this figure as an Autobot at all. There's the garish royal purple and red colours, the scowling face, the crown motif, the pop-out horns, the flaming brand and matching heart-stone, the spiked and toothed shoulders, the beast fur that looks more like quick-silver than anything organic, the almost baroque clockwork details, all combining to make this a fearsome vision.

And then, replace his severed head with his namesake Prime Master, for extra power-lust, inscrutability and schlock.

Amusingly, as I was writing this my current playlist started playing Gimme The Prize by Queen ("Here I am! I'm the master of your destiny...").