Half-Life 2: Episode One

Originally titled Half-Life 2: Aftermath, Half-Life 2: Episode One is the follow up to the original Half-Life 2, featuring pretty-looking HDR effects, more cooperation with Alyx, more physics puzzles, and red skies o' doom.

As of 16 November 2024, Half-Life 2: Episode One has been merged into base HL2 as part of the 20th Anniversary update, with its Steam store listing now removed.

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Development Info Prerelease Info

Unused NPCs#

Ministrider#

Watch on YouTube The Ministrider (npc_ministrider) is an enemy available in pre-Orange Box versions of Lost Coast and Episode One, and is an early version of the Hunter seen in Episode Two. It was briefly used during Mossman's transmission in the chapter Direct Intervention, but was removed and replaced in favor of a scripted npc_furniture entity after both games were migrated to the Source 2007 engine branch. The code for the Ministrider was never included in any release of the Source SDK as Episode Two was still under development, and as such only appears in early release builds of Lost Coast and Episode One.

The Ministrider has 300 HP, can keep track of known enemies for up to 60 seconds before forgetting, fires AR2-like bullets of type MinistriderGun, could fire charged "sonic blasts" that apply an initial physics impulse of up to 50,000 Hammer units, and is vulnerable to explosives, physics prop damage and Combine energy balls. Ministriders would have also been able to duck to cover; both the charged sonic blast and ducking ability were removed in the final version of the Hunter in favor of charging into and meleeing enemies.

There are only four available sounds for the Ministrider, all comprised of footsteps and alert noises repurposed from the Combine Strider; the rest of the sounds for this NPC are missing. Error messages relating to this issue can also be involuntarily triggered in the Arctic transmission sequence as well.

Hackable Manhack#

Watch on YouTubeManhacks were originally intended to hackable by Alyx, in a similar way to how Rollermines could be hacked during the early chapters of Episode One. Code for this variant of the Manhack exists in game/server/hl2/npc_manhack.cpp, and would have carried the following attributes and behaviors:

• Converted Manhacks carry relationship class CLASS_PLAYER_ALLY (effectively turning them into allies), but are still vulnerable to all damage sources originating from the player and NPCs
• Utilizes green LEDs to distinguish hacked Manhacks from their Combine counterparts, even if engaged in combat
• Idles if there are no nearby enemies or none exist in its line-of-sight after being released from the player's gravity gun
• Does not destroy itself after a period of time unlike hacked Rollermines, which carry this capability
• Manhack engine speed is 2× that of the unhacked version, allowing them to fly faster in swarms

The only code change required to enable hackable Manhacks is to modify the boolean function CNPC_Manhack::CanInteractWith() to return true in line 158 of game/server/hl2/npc_manhack.h, as it was deliberately temporarily disabled by a Valve developer in code. Hacked Manhacks do not insert/emit the appropriate danger sound to scare off enemies, which can confuse Alyx and other ally NPCs into a fleeing state simply by being told to convert a Manhack.

Hackable Manhacks were originally intended to appear in place of a single Rollermine during the first map of the chapter Urban Flight (ep1_c17_01), based on the existence leftover devshot cameras located inside of the coffee shop (all starting with the prefix manhackbuilding) and the presence of several scripted entities, which include an unused VCD look target (where Alyx would have observed Manhacks flying into the cafe) as well as an unused Antlion template NPC named antlion_forManhacks (spawned by template entity ptemplate_AntlionsManhacks).

No reason is provided for this NPC's removal, but it is possible that hackable Manhacks were disabled in favor of hackable Rollermines, as the former does not perform well in large combat encounters involving groups of Combine soldiers, in addition to the danger sound bugs that caused NPCs to flee away from friendly Manhacks and unusual movement behavior when released in an environment where no enemies exist, making it particularly easy to lose a hacked Manhack.

Scrapped Sequences#

Watch on YouTube

Stripped Soldier#

During the Citadel escape chapter, Alyx and Gordon come across the lifeless body of a stripped Combine Soldier. Frustrated, Alyx expresses her anger by mocking the soldier, and kicking the corpse off the edge. This scene has two variations.

Subway Map#

After emerging from the underground, Alyx was originally meant to point out a map in the room and remark that they still had a long journey ahead before reaching their destination.

Combine Outpost#

During the segment where the player storms a Combine Outpost, Alyx jokes about breaking "about 50 Combine regulations." While this line remains in the game, she was originally intended to humorously list a few of the rules they had violated off the top of her head.

Exploding Console#

Matt T. Wood, a former level designer and choreo director at Valve, has a developer commentary describing a scrapped sequence between Alyx and Gordon that was meant to take place before the puzzle room with the Stalkers and Rollerminers.

"In an early version of this map, Alyx led the players through the whole thing. To make Alyx seem less omniscient, we had her access a console here to get her bearings. It exploded, which helped drive home the point that the Citadel was in bad shape, but generally, it was a long pause in the action without a lot of payoff. After we made the high-level decision to have Alyx follow the player, this entire scene became irrelevant, and we happily cut the whole thing."

weapon_proto1#

In ep1_pak_dir.vpk, inside of scripts folder, there is a weapon script for a prototype weapon called "weapon_proto1". More information about the weapon and its specifications are here.

Unused Maps#

ep1_citadel_00_demo#

Judging by its filename, a version of the starting map made for a demo version. The released game does not have a demo available. Loading the map via developer console causes the game to crash, and decompiling the .bsp file via programs like BSPSource spits out errors. This map was accidentally released to the game with the SteamPipe update.

wasteland_test#

Watch on YouTubeA map called wasteland_test.bsp was included in an update to Episode One in May 2013. It takes place in a barren, rocky canyon, infested with Fast Headcrabs and Antlions. The map features an apparent Resistance base, two small outposts - each with three supply crates, a nonfunctional Emplacement Gun, and two rebels - one manning the gun, other, armed, providing medkits, a hill in the middle, and three Striders at the end, non hostile unless attacked, and separated from the main area by a deep ravine. The player spawns in the Resistance base guarded by four reprogrammed Combine Sentry Guns, and containing two Health and two Suit Chargers, as well as three supply crates and an infinite grenade crate; a reusable TNT trap is located near the base. He is greeted by an on-screen message from Alyx, who says that she needs six petrol cannisters, scattered around the map, to fuel a chopper, and that the player has to "find them and put them in the receptors by the cave entrance". Although Gordon has the Scout Car at his disposal, he is attacked by a never-ending wave of Combine Soldiers and Elites deployed by Dropships. When the player manages to collect all of the canisters, Alyx says that she needs to "make a few more repairs", and tells Gordon to "hold them off" for as long as he can.

Vortex Hopwire Grenade#

Watch on YouTubeThis "weapon", also nicknamed the Black Hole Grenade, can be spawned through the console. It is very powerful, drawing everything nearby into it before collapsing and killing enemies instantly. However, it is glitchy and has an unfinished model; as it re-uses the Rollermine model as its worldmodel and the Frag Grenade's viewmodel. According to Episode Two's commentary track, this would later become the Magnusson Device.

If used too close to Alyx, it can kill her and spawn endless ragdoll copies, and often crashes the game to desktop. Later in few updates, code and scripts for this weapon were removed, however, it can still be spawned via console commands in Portal.

Unused Textures#

Early blue Vortigaunt texture#

This is (presumably) an early texture for the vortigaunts seen in the intro.

Chapter 6#

This GUI texture is for the obsoleted 6th chapter named Coming Soon. It shows Alyx hanging on from a metal railing from a train, something that can be seen in the Episode 2 teaser found in the game files.

squashed parts.vtf#

Found in materials\models\antlion_grub, this is an early version of the grub's squashed parts. Note that it doesn't have an underscore, despite being 2 words (squashed parts).

vortring#

A sprite for the vortigaunt ring.

sky_day03_06c#

An alternate variant of the skybox used in d3_breen_01 from Half-Life 2.

sky_ep01_01#

A daytime skybox with the red ring seen in the other skyboxes. Its use is unknown, though.

Antlion Guard#

Two Antlion Guard textures can be found within Episode One's files. These textures give the Antlion Guard a blue-ish colour. These could be early versions of the Antlion Guardian's textures from Episode Two.

Combine Monitors#

Various temporary textures of Combine Monitors can be found in materials\effects. These consist of photos of the main characters. Gordon's picture seems to be taken from concept art.

Unused Model#

models/props_outland/pumpkin01_explosive.mdl contains an untextured pumpkin from an early build of Episode Two.

Unused Dialogue#

Citizens#

G-Man#

There are various soundscripts located in Half-Life 2: Episode One that are pre-loaded, but whose respective sound files were omitted in versions after the preload release. The G-Man is one example of this. Here are various lines from the intro, and his only appearance in the game since the Vortigaunts hinder him from getting to talk to Gordon. Seemingly, he was to speak with Gordon in early revisions before being cut off, whereas in the final he is instead stopped from even initiating conversation.

Alyx#

Barney Calhoun#

Unseen details#

During the arctic transmission, there are two details that go completely unseen without the use of cheats.

• Outside the base, the game spawns two elite Combine soldiers along with a standard Combine soldier positioned outside. This soldier is only visible through the use of cheats or, if developer mode is enabled, by activating the commentary note that talks about the room. Thanks to the new camera angle provided by the node, the player is able to spot the soldier outside.
• Inside the building, there is an empty room to Mossman's left. In this space, the game spawns an invisible NPC responsible for delivering dialogue for the rebels.