A monster or an evil entity that does criminal or evil acts. If something goes wrong, its usually because Grease Goblin did it.
Niko: Someone stole my car and drove it into an orphanage
Alex: It was Grease Goblin....
A grease goblin a person who doesn't shower and watches Hazbin hotel and my hero academia role play
Oh my fucking God Charlie is a total "grease goblin"