Every once in a while I do an illo and it never shows up again, presumably because the card it was painted for got eliminated in gameplay testing. If anyone knows this card, let me know 'cause I've never been able to find it!
EDIT-- Seems this was a card for the MINE CART RUSH boss encounter in the League of Explorers adventure. They list the encounter in Hearthstone Wiki, but no card is linked. Anyone have any experience with this?