Killer Instinct and Serial Killer Achievements

Create a private lobby and invite your friend. Pick one of the smaller maps to speed up the process of farming kills/wins. Set the round to 5 minutes with 10 points required for a win. Hop into the game. The Predator is a good way to quickly farm the wins because he can easily one-hit enemies at a distance and his vision modes allow you to find your buddies even faster. Farm the kills and you'll get those pesky achievements in roughly 30 minutes.

Obviously you need a buddy willing to let himself get killed over and over again to get the achievement.