After the account had been compromised, Riot Games president Marc "Tryndamere" Merrill leaked a potential card game being released based on League of Legends.
While the screenshot may look a bit rough around the edges, Riot were indeed allegedly planning to release a new game or game-mode and have been spotted purchasing domains containing the name in it. The individual who hacked the account mentioned that the game was fully complete but not released. Said account thief willingly returned Marc "Tryndamere" Merrill's account back after various additional leaks.
Here is a list of domains suggesting that "Supremacy" may be in effect:
leageoflegendssupremacy.net
leagueoflegendsupremacy.com
leagueoflegendsupremacy.net
leaugeoflegendssupremacy.com
leaugeoflegendssupremacy.net
lolsupramecy.com
lolsupramecy.net
lolsupremecy.com
lolsupremecy.net
lolsupremicy.com
lolsupremicy.net
All domains were registered several months ago. With the rising popularity of Hearthstone, it's very likely that Riot is focusing their energy down this avenue. Here is the leaked screenshot of the alleged "League of Legends: Supremacy."
EDIT: The compromised Twitter account has just updated its followers with a plethora of images in an imgur album, showing various card templates.
Source - Twitter?