Originally Posted by promaori
The way I see it, overkill's are only obtainable legitimately during an Oddball match when you have the upper hand. But if everyone is keen to try it out, I'm more then up for it. My trueskill rank on Lone Wolves is ~41.
I got mine out of pure luck more than anything else, but yeah, oddball is your best shot for Overkill, Killtacular and Extermination.