It was introduced in the Call of Duty: Black Ops Zombies map Moon. It allows the player to hold three guns at once.It costs 4000 points to buy,making it the most expensive Perk-a-Cola available to date.When purchased, the player won't see any effect except for the symbol appearing in their HUD. When the player goes to buy their next weapon, the prompt will still state that taking it will replace the currently selected weapon, but in reality it will take its place in the third slot. The weapon in the third slot is not always static and sometimes changes.That,because if a weapon in slot 1 or 2 is pack-a-punched, when that upgraded weapon is re-acquired from the machine,it does not return to its original slot as expected,but rather it becomes the new weapon in slot 3(and this can cause some confusion later if downed and an unexpected weapon is lost.)
It's HUD color is dark green, yet when it is drank it appears a dark red.
In the update that took place on September 27, Mule Kick is now available on all maps for PlayStation 3 and Xbox 360. It came to PC along with Patch 1.15 on October 11. However, the player must be connected to PlayStation Network, Steam or Xbox Live for Mule Kick to appear on other maps than Moon.