The original mod was for Doom 1.666 and had to be patched over the game, replacing the second episode The Shores of Hell. It turned out to be an excellent choice, as the music tracks well complemented the levels' atmosphere; especially for E2M2 and E2M6, when the Marines first enter the Atmospheric Processor, and when Ripley returns there to search for Newt, respectively. Fisher later adapted Aliens TC for Doom II.

The load screen retains that of Shores of Hell. A new load screen was among the numerous improvements never implemented, as Fisher had worked on the project for around six months and was sick of it at the end.

Most of the textures are techbase. The background uses Knee Deep in the Dead's misty, mountainous skyline. Fisher also cleverly used hellish textures, colouring them green, which made it look convincingly like wall slime.

E2M5 "Escape from the Atmospheric Processor" was suppose to after E2M2 "Atmospheric Processor". However, Fisher had to shift it so that the secret level would work properly, as E2M5 leads to the secret level in Shores of Hell.

E2M5 and E3M1 are designed for deathmatch, as they have proximity indicators that lower and flash when a player walks by. Most of the levels, however, are generally non-linear with the exception of E2M3 (sealing off the MedLabs and getting to the transmitter).

"Escape from the MedLabs" was split up into E2M4 and E3M1, the later being a bonus level. E3M2 (the Alien Ship) is another bonus level which was made by Fisher's friend Richard Love.

The "regular" aliens are based on the Demons and take approximately 2 shotgun shells or 14 bullets to bring down. This was a key reason why AliensTC was difficult, as it took much (scarce) ammunition to kill these common enemies, which could run fast and could do significant melee damage.

Aliens that spit acid use Imps. While no member of the species so in the actual Aliens universe, Fisher said he wanted to add variety.

Aliens that explode and release corrosive acid were made by using a Spectre and exploding barrel, which several reviewers considered very innovative. Consequently, due to the limited damage frames in Doom, there are no regular exploding barrels in the TC. The only clue that an Alien would burst is that it makes no sound.

To implement the hatching eggs that release face huggers, Fisher had the Cacodemon release a Sergeant, not unlike how the Doom II Pain Elemental releases Lost Souls.

The Queen Alien (replacing the Cyberdemon) graphic was a poorly digitized version of a model, as Fisher conceded.

The Pulse Rifle was the most common weapon in Aliens (1986), while the shotgun only makes one appearance, being carried by Corporal Hicks "for close encounters". However, the shotgun tends to be the most widely used in Aliens TC due to the availability of shells.

The Grenade launcher is underslung on Pulse Rifle, so both weapons are acquired with one pickup. Both also have the same first-person graphic, save for the LED counter which is green to indicate the Pulse Rifle and red for the Grenades. (In the movies, the ammo indicator is located on the side of the gun.)

Fisher describes the Smartgun as a "2 meter electric monster carried by Drake and Vasquez", and has it firing small yellow energy pulses. In the movies, the Smartgun is merely just the squad's machine gun, with its only electronics being its limited auto-aiming capability.

Fisher designed Weapon #7 to punish cheaters, so it will simply show images of the Power Loader but not do anything.

"Check these corners. Check these corners." Sergeant Apone as the team carefully inspects the premises.

"Remember, short controlled bursts." As the Aliens are breaking into the MedLabs, Cpl D. Hicks reminds the Marines that they don't have much ammo.