Lux Ultimate + (Enemy) Nautilus Ultimate
Watch MattLeague's stream highlight: How did i hit nautilus for 645 dmg and kill him? I wasnt aiming anywhere near him - Plays.tv
Encountered a very interesting bug while reviewing a recording of a team fight. As you can see, the enemy Nautilus is in the baron pit fighting my team's Amumu. He casts his ult on me, and as it begins to travel, I cast my Lux ultimate. As i get knocked up, my ult finishes casting. It seems that because I was in midair when the ult finished channeling, it did the damage to Nautilus regardless of the fact that he was NOWHERE near any of my abilities at the time. As you can see in the video, as i cast my ultimate Nautilus takes 600+ magic damage and I get credit for the killing blow. Interesting.
and 
if you ult in a random direction then flash the direction you want it to hit. the ult will hit the direction that you flash and i think that because the 
knocked you up it caused your ult to redirect towards him.