Energy grenade mortar
The Mortar Synth is an incomplete Half-Life 2 aerial enemy only glimpsed towards the end of the game in the Citadel on several conveyor belts along with two Crab Synths, during Gordon Freeman's second pod ride. It is unknown where they were transported to, as they are never encountered in combat anywhere during the game or its episodes. With the Crab Synth, it is said to be "the backbone of the Combine's subsequent armies".
The Mortar Synth consists of a fleshy, triangular body with a mortar located on its back. Its front end features many spiked protrusions and various mechanical systems. Hovering low above the ground, it was to use its mortar to throw "energy grenades" flinging upwards its rear section, similar to a catapult. It was likely to be used as a support infantry by the Combine, its attack allowing it to hit only far targets, being inefficient at close range (according to the file "skill.cfg" in the Half-Life 2 files, its energy grenades were to have a good range, but only inflict minor damage to targets).
Behind the scenes
- The Mortar Synth was never completely finished and seems to bear a temporary name, likely related to its use of a mortar (with the Crab Synth, it is one of the only Synth to have "Synth" in its name). It has incomplete animations, model errors, both high and low quality textures and missing files. This is likely why it is only glimpsed and not confronted during the game.
- It is likely one of the earliest created Synths (with the Crab Synth), when they bore more red and yellow and did not feature any Combine logo (see also the original Dropship). Ted Backman subsequently defined the current design, with more blue and more pale colors.
- The player was originally to directly confront the Mortar Synth in several situations; in the Skyscraper and during the City 17 uprising, among others.
- The Mortar Synths seen in-game are not actual NPCs and are simply "cycler" entities designed for testing animations. As a result, they cycle through animations when shot and can be paused and unpaused by pressing the "use" button on them.