He will unlock Ortensia's House so that Mickey can go inside. Inside he will find a bunch of sad Bunny Children that miss their mother and Ortensia's Locket. Mickey can trade it to the Museum for 250 E-Tickets, failing the quest. Or he can give it to Oswald, completing the quest and earning him another health pip.
Giving the locket to Oswald will no longer be possible once Mickey returns to Mickeyjunk Mountain to confront the Shadow Blot. He can however, still give the locket to Laralee inside of the Museum even after dealing with the invading Bloticles in Mean Street. However, if he doesn't do anything with the locket before heading to the Battle in Tomorrow City, the quest will expire.