Pogo has re-released 50 previously-retired Mix-n-Match badges today. These badges cost 12 gems each and are available until April 5th, 2019.
These badges were originally released in September 2000 and December 2018.
https://www.pogo.com/challenge/find-badge.do?searchtype=mnm&sortName=expires&sortDirection=true
(https://i.imgur.com/eiEK1Ge.gif)