Lucifer

Lucifer is a boss unlocked at level 15, and he spawns every 8 hours. You can not use your troops when attacking the Lucifer, but you can invite up to 5 friends. These can be very usefull if you have a friend(s) that are a lot better then you, as the lucifer gets harder to beat every time you level up.

Strategy

Spoils
The higher level you get, the more xp Lucifer will give, starting at around then 5000, going higher up the more times you kill him. He will aslo drop lucifer orbs, which when you collect 200 of, you can then get the Lucifer sword. He also drops gems, starting at a measly 3, but going up very high, up to over 20.