The Gary Friedrich situation caused much furor amongst comic book artists, wondering if they were at risk of any future action by any publisher for drawing and selling sketches of their chatracters at a comic convention. Marvel tried to placate such fears but without any blanket statements that Marvel or Disney would not legally target anyone sketching and selling Marvel characters now or in the future, many remained… unplacated.
It's not blanket however, those who have been contracted at one point to provide artwork for Hasbro are free to sell such work. But wannabees are forbidden.
Visual from hd-esign