I got one from my mystery melody today, and I was wondering what it does? Anything you can tell me about it will be appreciated. Thanks ^_^

It adds anywhere from 1-3 spaces to your pet's Treasure Chest when you select 'Open For (petnamehere)'. Congrats, that was very generous of your MM!

when opened for one of your pets, the box increases your pet's Treasure Chest slots (:

and

Alrighty, thanks guys ^^ And yeah, it was pretty nice, wasn't it? :)

I am so jealous. :c my MM NEVER sent me anything [i try to join everyday and then I start sending itens], not even a random item.