6. The Gel Guards - The Three Doctors (1973)
You can sort of explain this one away by the fact that the Gel Guards are products of the insane Time Lord Omega's mind but they're still pretty dumb despite that. Apart from stalking the Second and Third Doctors and their allies through a typical BBC quarry and having a brief battle with some UNIT soldiers, they never really do anything. They were always going to be second fiddle to Omega but even then they were just filling space without anything to make them really stand out. And of course, they looked really stupid, sporting light-up claws that cause distant explosions (their main weapon) and resembling cycloptic postal sacks with severe acne. A missed opportunity in both appearance and actions.