2. The Aether (Malekith)
Christopher Eccleston is a superb actor, so it really was a shame to see him wasted as Malekith in the Marvel Cinematic Universe. He was the main villain in 2013's Thor: The Dark World and he had a plan to use the Infinity Stone known as the Aether to plunge the entire universe into darkness and restore his race of Dark Elves to dominance. Of course, he failed, as the combined efforts of Thor, Jane Foster and Erik Selvig saw him transported to the realm of Svartalfheim and crushed under the weight of his own gigantic ship - but that's not how he should have died. Malekith was weak as hell (the poorest villain in the MCU, undoubtedly) and shouldn't have been considered powerful enough to wield the Aether in the first place. It should have vaporised him when he tried to harness its power, as that would have emphasised just how powerful the Infinity Stones are - something that the MCU has spectacularly failed to really get across so far.