Malefor is actually a really sadistic and evil villain when you think about it. He kidnaps Cynder, and others (If Oc's are to be considered here), He almost succeeded in destroying the world the last time he was alive, technically did when he returned, corrupted Spyro, corrupted Cynder, ransacked the temple, almost obliterated the dragons, is so evil that his voice has been warped by his malevalence, and he kills because he could care less. He also inadvertably causes the death of Ignitus, effectively destroying Spyro's mentor, friend, and father figure and causing him to go ape on Cynder. What a perfect A-hole. I actually find it difficult to think of worse villains.
If some Fanfic's are to be considered, (like the one I'm working on) he was actually even worse than he was depicted in the game. Seriously, he is crazy evil. No matter how you look at it.