The Nilbog at page 182 in Volo’s Guide to Monsters has the following feature:
Nilbogism. Any creature that attempts to damage the nilbog must first succeed on a DC 12 Charisma saving throw or be charmed until the end of the creature’s next turn. A creature charmed in this way must use its action praising the nilbog. The nilbog can’t regain hit points, including through magical healing, except through its Reversal of Fortune reaction.
So if anyone would use the a Wand of Wonder, even the nilbog himself, would they have to make a Charisma Save before using it if there is a slim chance they could harm the nilbog?
If the nilbog would use it, there are a lot which could happen to him: stunned on a 11-15, potential 1d6 psychic damage on a 21-25, potentially standing in a fireball 70-79, blinded on a 91-95, petrified on a 98-00.