The Twitter account belonging to Riot Games' Mark Merrill was commandeered by a hacker. During the takeover of the account, a game called League of Legends Supremacy was revealed. The information included images of the game that viewers have compared to Blizzard's Hearthstone.
We're always working on a variety of new ideas for League & beyond. Lots of experimentation that may never see the light of day :)— Marc Merrill (@MarcMerrill) October 13, 2013
After reclaiming his account, Merrill confirmed that the game was (is?) a work in progress that he considers "experimentation that may never see the light of day".
Read more at Gamebreaker.tv