6. The Dark Wanderer jabs himself in the face with the devil's soul (Diablo)
We'll give the Dark Wanderer this much: He honest-to-God tried. See, at the end of the original Diablo, Aidan, as he was then known, had successfully gone mano-a-mano with Diablo, the Lord of Terror himself. His victory meant Hell's maw had shut, for the time being. However, Diablo's not one to stay down, so Aidan had a choice to make. On one hand, he could devise a clever solution to keep Diablo contained, a solution akin to the demon's original Soulstone. On the other hand, he could just man up.
So he did what any good hulking brute of a warrior-man would do: He jammed that sucker right into his own forehead. Seriously, who could've guessed that taking a giant, pulsating shard--a shard that contained the imminently corrupting essence of evil--just taking that thing and ramming it right into one's skull would be, in fact, the incorrect option? Long story short, he failed. Diablo thus back in the world, the Dark Wanderer then heads off and frees Baal, The Lord of Destruction. Fun times.