An upcoming videogame called Young Justice: Legacy is supposed to help bridge the gap between the two seasons. The tagline for the game is "one will rise, one will fall, one will die". Speculation is that Artemis dies while Kid Flash becomes the Flash (rise) or melds with the speed force (fall) while Aqualad becomes Aquaman (rise) or Black Manta (fall). However, the show creators have been lame about this previously when they said someone that "no one is safe and someone will die" in Season 1. That turned out to be Kent Nelson (original Dr. Fate host) who only appeared for that one episode.
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-Merc