Cornelious looks up at this monstrosity, and knows fear. Having already been weakened from being crushed by a boulder, Cornelious knows there's no way he can take this thing head on. Looking around the room for an avenue of escape all he can see is the smokey wall behind the demon. The way behind him also leads to an eternity of death, hollowing, and madness. That left only one option. Cornelious started running at the demon while muttering under his breath, as he gets to within 15ft of the demon, a silvery mist surrounds the mage until he's out of sight. Poof! Now 15 ft behind the demon Cornelious makes a mad dash for the smokey wall.
OOC:
so I cast misty step as a bonus action and used 20ft of my move action to get to the wall, if I can go through it I will and I'll use my main action to run as well