The Elf Cannon was a limited time decoration released on December 24, 2014 during Part 2 of the Christmas 2014 Event. Once completed, it allowed the player to shoot Elves in Bottles to "deport" the Elves and earn Elf Bells.
Similarly to the Castles during the Clash of Clones 2014 Event, the Elf Cannon had upgrades that could be applied to it. Each upgrade raised it a Level, and each Level added a new effect to the Elf Cannon to improve it.
The Elf Cannon had three different skins to it which were automatically changed as the player Leveled it up. Each upgrade could be bought with Cogwheels. As the Levels increased, the cost of each upgrade increased. There were a total of 20 Levels that the player could upgrade the Cannon, and any Level beyond that was simply for "bragging rights".
The player could not "deport" Elves infinitely though, as after three shots, the Cannon had a cool down time. No matter what Level the Cannon was on, the player always had three shots between cool down times.
At its original Level (without upgrades) the Elf cannon could fire 9 Elves in Bottles at a time, and each Elf in a Bottle paid out 2 Elf Bells. In total: 18 Elf bells per 9 Elves in Bottles. The player had 3 shots for the cannon before a cool down time began. The cool down time started at 3 hours and 45 minutes and could be decreased by leveling up the Cannon.
Upgrades could only be applied to the Elf Cannon once the player won the Cannon Control Building. Upgrades could only be applied from the Control Building which displayed the "Elves per shot", "Bells per elf", and "Cool down" time, depending on the current Level of the Cannon.