The legendary Monkey Claus is not a tower nor a Special Agent, but more of a game event that only occurs in the two weeks of Christmas. When the event is on, every 3 - 10 minutes of gameplay the Monkey Claus, a monkey on a sleigh with reindeers, will fly across the screen and gives you 2 free towers, special agents or upgrade pack for one of your existing towers (only 1 if the upgrade pack is very expensive, like Aircraft Carrier, Ray of Doom... the Temple won't be awarded). He can also use his huge bag to capture ALL the bloons and MOABs (no stronger blimps) he comes across and send them to infinity on his way! You'll meet him more often if you have more Monkey Towns. (reference?)
- The reference just can't be more obvious.