Once my tamagotchi turned into an old guy and the WEIRDEST THING HAPPENED. I went to feed my tamagotchi a snack, and you could EAT A BALL. . I ate it 3 times, then it went back to normal and the edible ball was gone I still had it on my items, fortunately!
I've only used the chest once. When I did, smoke came out and my girl tama, who was a toddler, was changed into the old woman tama and was mad. Then ALL her Hungry and Happy hearts were empty. She changed back to normal after about 15 seconds.