Final Boss Veigar, I can think of someone who's a bigger troll than you...
Two words: Yuki Terumi.
What an evil son of a b!tch. Cruel, sadistic, and insane beyond measure. Delights in the physical and mental suffering of others, relishes chaos, and generally just loves to f%ck people over for kicks.
And that laugh of his...
https://www.youtube.com/watch?v=GTCFLikQf_8
Goddamn, that gives me goosebumps.
I might not have a kit in mind for someone like this, but at the very least, Riot needs to make a Champion who fits this personality and story. Draven might be an ass, and Veigar might be a little turd, but Terumi? Impossible not to hate him.