Board Thread:Questions and Answers/@comment-24310213-20131218225741/@comment-24203473-20131218235014

This was a feature that was added in at the same time that Shugabush Island was revealed, all it does it let you buy back the last monster you have sold on that island. The monster that you buy back will be the same level as the one you sold.

It's basically there for those times when you accidentally sell a monster you didn't mean to. Not that I've ever done that... >_>;