Synth

A Synth is a self-replicating robot that evolve. Originally organic or cyborg creatures, Synths were taken over by the Combine through their conquest and wars and enslaved to be turned into war machines.

Overview
It is unknown how much of the Synths presented in the series is original to their initial species or added by the Combine, since the Combine forcefully modified their appearance by adding mechanical equipment and weaponry, while keeping enough biological parts to let them self-replicate. It is also not clear whether they originally were fully organic or were already cyborg creatures when the Combine took over them, and if they all come from the same planet (mirroring the Xen creatures that were also brought from other worlds and, for some of them, also enslaved). It is also suggested that some were created from scratch by the Combine.

Their carapace-like flesh is immune to gunfire (with the notable exceptions of the Hunter and Shield Scanner) and hitting it produces a metal ping noise. These outer shells can be ripped open with enough force, as demonstrated when Dog tears a Strider's head open in Episode Two. Other than this, the only thing that can effectively kill the larger Synths are explosives from the RPG, the MP7's secondary fire, a Combine Energy Orb and the Magnusson Device.

It is likely that Synths were the primary forces used by the Combine during the Seven Hour War as the human-derived Combine units, such as Hunter-Choppers and APCs, would have only started appearing after the Combine rule on Earth had been established.

Types
Various types of Synths have been brought over to Earth by the Combine, and more Synths probably exist elsewhere. Some are merely used as scouting or transport and have little to no weaponry, while others are fierce war machines.

Known Synths

 * Advisor Pod
 * Combine Dropship
 * Combine Gunship
 * Crab Synth
 * Hunter
 * Mortar Synth
 * Shield Scanner
 * Strider

Behind the scenes

 * According to Dhabih Eng, the team tried to incorporate elements that were neither strictly organic nor purely mechanical to suggest their original organic forms. They did not want to have giant alien creatures with armor attached or implants added, but rather show a forceful evolution of the equipment unnaturally imposed on them by the Combine. In the end, the designs intentionally blurred the line between machine and animal, in their appearance and more importantly their motion and how they reacted to the world around them.

Cut Synths
Several Synths were cut from the final version.


 * Combine Guard (part-human, part-Synth)
 * Combine Super Soldier
 * Combine Synth Elite Soldier (part-human, part-Synth)
 * Sacktick
 * Wasteland Scanner

Early Synths
Several pre-release materials gives some insight about the early Synths.

Weather Control story fragment


Raising the Bar features a story fragment of the Weather Control chapter given to the developers for design inspiration, relating parts of the Weather Control battle, with early names for the Combine units. For example "mech" seems to stand for the predecessors of the Synth, while "mech carrier" likely refers to the Combine Dropship. The text depicts the mech looking like Dog's cousins, but apparently new-minted and flawless, and with a "head" in quotes, suggesting that it is strangely-looking. Also, at some point in the text, its head pulses with a faint glow as if powering up for energy, then fires, which is very similar to the Strider's warp cannon, added to the fact that it is brought by a "carrier", the Strider being brought by Combine Dropships without their containers. Added to the gun located in its head, it also has mounted guns. This "mech" could be an early version of one the Synth predecessors of the Overwatch Elite, the Combine Synth Elite Soldier, which has been through several iterations with strangely-looking heads and a narrow waist like Dog (as in the picture seen here), or the Combine Super Soldier, also with a strangely-looking head.

"TBot1"
A folder called "TBot1" can be found in the model textures files from the playable Half-Life Beta files, in a folder called "obsolete". This is likely the textures for the early "mech" or (ro)bot from the Weather Control story fragment, a very early NPC, since it bears some similarities with Dog in design, mirroring the Weather Control story fragment covered above. Since Dog is said to be one of the few concepts that went from the first sketch straight into the game with relatively few changes to the design, it could be assumed that the Weather Control mechs are two legged and bear similar colors and same bodypart plates than Dog, since he was made from scraps from different metal sources, such as Combine metal (Old texture files for Dog also show some sort of early Combine logo also found in the TBot textures).

The textures also suggest a slightly battered robot, show round eyes that recall the City Scanner's eye, and therefore Dog's head, and is overall yellow-colored and seems to have paws-like feet and two legs, also like Dog. The model is however missing, and it is next to impossible to guess its shape from its texture files. The "1" in the folder's name also suggests that there was probably other versions, thus other colors or other conditions, for example non-battered textures. Other texture files suggest that it had an antenna and was equipped with a flamethrower and that some of its intern circuits were to be visible and blue, like the early Behind the scenes|Combine Dropship, the Crab Synth and the Mortar Synth. The files also suggest a "collar" made of green fabric, with the same fabric on one shoulder and the thighs, which seems peculiar, although it is another example of the old concept of the Combine recycling human materials.

This "TBot" ("bot" implying "robot") seems more mechanical than Synth (sporting several cogwheels and pistons on its bodywork), more in the "Combine recycling the human materials" mood of the very early Half-Life 2 storyline and very closer to the "mech" from the Weather Control story fragment, therefore its model was likely an ancestor of the two-legged Synths of big size, the Combine Synth Elite Soldier or the Combine Super Soldier, with strangely-looking heads.

Alyx story fragment
A story fragment from Raising the Bar is set at the start of the Air Exchange chapter and has Gordon involved in a train wreck when arriving there. Alyx encounters him with her pet Snitch and they are attacked by "tripods" (i.e. Striders) and "Combine Elite", tall shapes looking like metal, and with muffled, almost silent movements. That does fit the description of the Combine Super Soldier, named "Combine Elite" in Raising the Bar, while the Combine Synth Elite Soldier could also fit, since it was also to be an elite Combine unit. As also stated in the book, the Elite was turned into the humanoid unit seen in the final version.

List of appearances

 * Half-Life 2
 * Half-Life 2: Raising the Bar
 * Half-Life 2: Episode One
 * Half-Life 2: Episode Two