Valve (on the whole) makes some damn impressive games. Adult Swim produces... interesting late night content on Cartoon Network. What could they ever have in common? The answer: Just enough for a collaboration. Adult Swim has recently posted this promo: Adult SwimThe post also encourages people to sign up for their newsletter ahead of time ("You've been warned."). So, what does it all mean? Is this the long fabled announcement of Half-Life 3? Left 4 Dead 3? Portal 3? Team Fortress 3? Ricochet 2? Something Dota 2 related? A brand new IP? My money is on them premiering the "Meet the Pyro" short, but this is Valve we're talking about. They just love surprising and trolling their fanbase. Only time will tell.