A. Common terminology used in such MMO RPG games as World of Warcraft, where a skilled player jokes about pwning a foe.
The term 'face roll' suggests that the person doing the 'face rolling' can beat their opponent by just 'rolling' their face along the keyboard, defeating their foe almost effortlessly.
B. "Face roll" can also be used a derogatory term, used when insulting another person's poor skills, or lack there of, when using their MMO RPG character.
The derogatory "face roll" term suggests the player used no skill what-so-ever and simply rolled their face along the keyboard.
A. Player: Wow, that guy is such a noob. I bet I could face roll him.
B. Player: Wtf was that dude? Did you just face roll that last boss or what? We wiped because of you asshole.