Kill Gods three times with your ultimate/4 in a single match.
The kills don't need to be all at once, it can be three separate times or a double and then a solo kill or any other mixture of kills as long as three of your kills are with the attack.
It's almost always a insta-kill when you land on a low health enemy that has the skull, certain special circumstance can prevent the kill like enemy getting a shield from some ability/attack or Kepri using his ultimate to save whoever you land on from your attack.