Deviling is a demon mini boss. It is not an MvP, so you will not get Guardian points for killing it.
It drops 
Black Dyestuffs (100.00%) which is an ingredient for making items at Justin and is an Alexa's Daily Quest item.
Card
Item ID: 4174
Name: Deviling Card
Description:
- Increases resistance against Neutral element attacks by 50%
- Reduces resistance against other element attacks by 50%
Compounded On: Garment
Drop Rate: 10.00%