Dark Cave Background. It was released from the plot (I think) so no more coming in to circulation - there are a few on SW under 90k, and a solid amount buyable... It matches with the new magma pets and is a kewl background. I think these could easily hit 250k with a bit of help. I've already bought a few, so I stand to make some profit too but also wanted to throw it out there (and help myself of course)