Time Warrior! Oh right, an obscure* Decepticon... I'd go for Octus. He transforms into a freakin' Dalek!
Don't forget to tell TakaraTOMY your wishes for future MPs on Q.38 in their online survey.

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*I'm going by the Obscure Transformers Web Site's definition of "Obscure" which means that the character must not have appeared in more than one medium. Death Cobra's a good choice too.