Half-Life 2: Episode 2 has a new record speedrun, accomplished in a stunning 30 minutes and 36 seconds with the help of various scripts. The segmented run was done in 441 different pieces on hard difficulty by the SourceRuns Team.
What exactly is going on here? Let this video from this year's Awesome Games Done Quick charity game marathon, performed and annotated live by a player who goes by the name Gocnak, be your guide.
Some of the tricks you'll see on display here are wall climbing, save clipping and accelerated back hopping — also known as ABH.
To wall climb, runners use the iconic gravity gun to pick up game objects and create ledges for themselves to gingerly mantle over the game's larger terrain features. Done correctly, this lets them cut out huge portions of some maps. To save clip, runners will get themselves stuck inside of wall geometry and then save and immediately reload the game. The Source engine then tries to un-stick the player by pushing them down just a little bit, allowing them to smash their avatar through barriers. Finally, ABH is a way of blindly jumping backwards through straightaways to pick up speed.
The most difficult part of this speedrun is, oddly enough, not breaking the AI scripting of your in-game partner Alyx. If you don't trip the right in-level triggers she just stops showing up, breaking the game and preventing you from completing it.
"This is one of the main reason nobody likes to do Episode 1," one of the commentators said during AGDQ. "It's basically Talking To Alyx Simulator, and we don't like Alyx."