A jwilson is a randomly re-named slime and somewhat of a joke. The creature has the same effects and attributes as a normal slime, including acid damage to metal items. They stopped spawning for a number of years but began reappearing around late 2007 or early 2008.

The source of the joke is from the early days of Ultima Online. Johnny Wilson, a writer for the influential gaming magazine Computer Gaming World, gave the newly-released Ultima Online a negative review. One or more of the Ultima Online game developers took revenge by adding the chance for a slime to spawn as a jwilson.