It's frustrating, because here you have a Transformer (indeed, Transformers; let's treat the Terrorcons as a whole here) whose alt-mode is that of a MYTHICAL CREATURE. You have massive scope for this being an interesting, fun character to play around with. Hell, I can come up with a story here off the top of my head. The Terrocons and Technobots (their Autobot Counterparts) get sent back in time to Ancient Greece. The Terrorcons, being all monstery and mythical, prey upon the superstitions of the time and get themselves worshipped, and plenty of Greeks doing their bidding. The Technobots however, align themselves with the great scientific and philosophical minds of the time, meld together even better as a team as a result, and kick Abomnius' ass. There. Wasn't difficult now, was it? Instead we got Carnage in C-Minor. There's no justice.
Sinnertwin then, as with all the Terrorcons, is a bit of a waste, fictionally. His Tech Specs are good, his toy is good, even the way he looked in the cartoon wasn't bad. He just had nothing to do. Which I guess is true of all the later combining toys, but it's still a bitter pill to have to swallow when the alt-mode is so awesome. At least he wasn't Blot, though.