Apart from the 15 weapon kills (all of them are in the manual, aside from the Troika and Boomshield), the unique executions are probably the hardest things to figure out. You must have an opponent on the ground and crawling to do these executions. Luckily, you can do them on any mode (campaign, horde, multiplayer, etc.). Anyway, there they are:

  • Curb Stomp -- BLUE button with any weapon.
  • Punch Combo -- YELLOW button with any weapon (except the ones listed below).
  • Neck Snap -- press GREEN button to take an enemy hostage, then context action to snap necks.
  • Any weapon (except the ones below w/ RED fatal) -- RED button fatality
  • Longshot -- YELLOW button fatality
  • Longshot (alternate) -- RED button fatality.
  • Boltok -- YELLOW button fatality.
  • BoomShield -- YELLOW button fatality.
  • Gnasher -- RED button fatality (hold while stationary over victim).
  • Torque Bow -- YELLOW button fatality.
  • Torque Bow (alternate) -- RED button fatality.