In the background story, Mixom mistakenly ships a number of chainsaws to the UAC base on Mars, in place of the requested jackhammers. The Doomguy eventually finds an e-mail which refers to a Mixom website, Mixom.co.jp (in the real world however that link is dead).
Looking closely in some cutscenes the player may be able to see the Mixom logo on the side of telephones around the UAC base. It also appears on doors, some computer terminals, and other devices, including the Delta experimental teleporters. Additionally, a newsreel plays on a TV early in the game (before all hell breaks loose) about Mixom and rival company Moxim suing one another for various reasons.
During the construction of Exis Labs on Mars, Construction Supervisor Travis Folsom wanted to use cheaper Mixom pressure seals for the exterior windows in the Environmental Sector, rather than the Moxim seals. The base architect argued that the Mixom seals were inferior to the Moxim ones, and would result in a breach. Corporate sided with Folsom, however, due to the cost savings.
The architect's predictions came true during the demonic invasion, when a Revenant fired its rockets at the windows in Environmental. The Mixom pressure seals failed and the windows shattered, resulting in a sudden loss of oxygen. Fortunately, a lone surviving marine from Bravo Team (the Player) managed to activate the emergency shutters and seal the breach in time.
Mixom returns in the 2016 reboot of Doom, where they are the manufacturers of the various doors on the UAC site. It is possible to also find its rival Moxim's doors and products as well. Mixom is also responsible for the new chainsaw model, PAINSAW, mostly used as a black market item at the UAC Mars Base.
In id Software's 2011 Rage, Mixom is featured as a remnant of the old world, operating a chain of gas stations among other things. It is one of several hints within the game that seem to indicate it occurs inside the same universe as Doom 3.