Agent 666 is the offspring of the devil, and the epitome of satan.

He was originally a guy called Lucifer who joined Deedle (with no powers or special abilities besides being a military dude) he was a fairly nice guy, until on his first mission when him and a team of expert Deedles including Johnny Pickles went to chop down the Hellspawn Tree because he found out Mecha-Satan was going to summon a Demon. (To find out more about this go on The Hellspawn Tree Wikia page.) They succeeded in chopping it down, but some of the sap from the tree fell into a cut he had got from fighting the demons that were guarding the tree earlier, and the evil tree sap travelled through his blood stream and possessed him while he slept that night, turning him into AGENT 666, a evil creepy super strong Mecha-Satan offspring that can light things on fire with his mind. First he pretended to be normal, until Monster discovered him and managed to kill him, before realising Agent 666 has 13 lives and each time he dies he becomes considerably stronger. Agent 666 then beats Monster easily then smashes his way through Deedle to get to the Hellspawn Tree to grow it back and summon the Demon. Deedle try to stop him though, and about 11 lives later when he is on his last life and EXTREMLY powerful and able to beat everyone in Deedle put together he regrows the tree and starts summoning the Demon, but Deedle stop that part. He and Johnny Pickles then fight in a church, where he is killed by being stabbed through the heart with the big cross (since holy things hurt him since he's the offspring of satan)