Which game had a villian so vile, so despicable, so (insert adjective here.) that you actually came to hate him/her. Not just want the good guys to win and everyone to be happy, but felt like you had a personal grudge against the villian and wanted him/her to die so bad you would do it yourself.
Mine would have to be Kefka from Final Fantasy Six. Not only did he poison a whole castle against orders, not only did he kill General Leo, not only did he shove his own Emporer off a cliff after striking him down. But he suceeded in his plans, took over the world, and ruled the land with his "
Light of Judgement"
from atop his fortress made out of scrap metal from the cities he destroyed. Plus his laugh ticks me off. Sephiroth is nothing compared to this guy.
And while were at it, how about Villian You Felt the Sorriest For. Mine would have to be Ganondorf from The Wind Waker. All he wanted has for his land to prosper. Deep down inside at least.
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Call me Citrus.