It's the villain of the Sleepwalker comic, the series Bob created in the 90s. Sleepwalker was slightly controversial because a poster advertised it as 'Sandman done right', since Neil Gaiman was just releasing Sandman around that time.
His name is Cobweb and as far as I know, he's only ever appeared in the Sleepwalker comics. Sleepwalker and Cobweb are also based on the Mindscape, a mental plane, which isn't technically mystical in nature. Cobweb probably has no connection to the Strange comic but it's awesome if it really is him used in the movie, even as a nameless enemy. Dr Strange and Sleepwalker did meet when Strange summoned him in two issues of the Defenders comics.
When I saw the enemy attack Strange and America, I couldn't figure him out. But the thread-like nature then when his bandage-y face appeared and when he restrained America, it really made me think it was Cobweb. Pretty awesome that he gets notoriety for killing a Strange variant. If that was him. Which I hope it is.
Bob Budianski has a ton of Transformers characters that he named that got on the big screen but Sleepwalker (and Cobweb) are all his tho).