Ortensia's Locket is a quest item.
After Animatronic Goofy is repaired, he unlocks Ortensia's house. Inside, along with five crying Bunny Children, is a locket bearing Ortensia's likeness. After collecting it and exiting the house, Goofy explains that Oswald gave that locket to Ortensia as a gift. Also, Laralee offered to buy the locket for her Museum. Goofy says it's probably okay to borrow it but encourages Mickey to return it later. However, the mouse doesn't have to do so.
Mickey can do the wrong thing and trade the locket to the Museum for 250 E-Tickets. Or, he can do the right thing and give it to Oswald. The rabbit will then begin to like Mickey (shown by calling him by his first name) and give him a Health Upgrade. It is noted that if Mickey talks to Oswald but refuses to give his brother the locket, Oswald will be furious at Mickey (exclaiming that the locket isn't even his) and go into his "bad" mood (with an angry face, crossed arms, and tapping left foot).