On a train of thought inspired by @Bebs' question, there are many one-off fun aliases made up for "off-contract" work : for example Luther Grosvenor as Arial Bender, Bob Dylan as Blind boy Grunt and so on.
"Blind boy Grunt" appears to have also been used by Janis Ian according to this article, so some overlap with the other question.
Is there a musician who is acknowledged to have used the most (different) one-off aliases ? I mean an alias used in credit for individual work on someone else's project, or for a solo work. If the musician's regular stage name is already an alias, that is included.