(Dead) Borax Tain
The party has meet Borax Tain on three separate occasions…
The first was at the Open Door Festival, where they dueled him (using a specialized deck of many things). They eventually defeated him and secured the Shining Blue Trapezohedron.
The second was a little while later at their inn. He seemed much younger and challenged the party to a game, Ronan accepted. He was defeated, but not without creating Jr.
The third time was when they found him time locked. Forever locked into the moment of his slaying of an Angel. He appeared to much older and mightier then his previous incarnations.
Upon freeing the essence of the box from the Island of Madness, the party was informed that all previous versions of Borax Tain were temporally dislocated versions of the real Tain. Now free of the curse, it is unknown exactly where and or when Tain is.
But it is clear that he bears some animosity towards Copperbottom for imprisoning one of his versions for many years. The two sides appear to be at war with each other.