There are a few easter eggs in Clash of Clans. Most are found in the Single Player Campaign, and range from special obstacles to secret traps.
There is an easter egg in the single player level Goblin Picnic. The player must place a jump spell on the P.E.K.K.A. statue, then place some ground troops to jump over the wall. The troops will trip on something, and Santa Claus will appear and drop down presents.
Three much smaller easter eggs can be found in the single player levels Gold Rush, Gobbotown, and Fool's Gold. If the player looks to the far left corner in Gold Rush, they will see an old Christmas tree from 2012. In Gobbotown's far right corner, a Christmas tree from 2013 can be seen. And, in the bottom corner of Fool's Gold, there is a 2014 Christmas tree.