Assassin's camp is, along with the Robber baron camp, purchased via a neutral entity: Al Rashid, in the Assassin's Fortress. It has the highest attack power (13), but also the lowest HP (200).
The assassin camp is rarely used because of its extremely low HP, but since it has a massive attack power, it can be used solely as a support during an offensive strike. Usually, one would first launch the attack with a high HP camp such as the baron or a large military camp, and quickly launch an attack from the assassin camp right after the first army arrived at its target. This will prevent the assassins from being harmed, unless if the large army camp is destroyed. But an assassin camp won't resist any attack for more than 20 seconds, making it useless for supporting allies in a defensive strategy and easy to destroy when attacked.If facing an enemy with an assassin camp, it is advisable to make it a primary target.