In the fifth mission in the PlayStation 2 port, the corpse of a guard can be found floating in a pool. The corpse has over 3,000 health and if hit enough times, it will destroy and spawn Snarks which can be acquired for use.

The ending of Half-Life: Decay can be seen from the perspectives of either playable character in the game, Gina or Colette. If you see the ending from Colette's perspective, a brief shot of a broken computer can be seen with red electrical arcs shooting out of it. Connecting these arcs in an emulator reveals the initials "MA", the signature of Gearbox Software level designer Matt Armstrong, and a symbol that he would often hide in games he worked on.

The game was originally planned to release on PC and it even had a completed port. However, this didn't happen. According to Patrick Deupree (one of the game's programmers), this was "due to powers beyond our control".

A fan-made recreation was released in 2008.