The Thing

The Thing is a mod made by Donald, back in 2004, Around a year after the game leaked.

Info
This mod is a real rarity, one of the first mods to be released for "beta" version of Half-Life 2. It's author, Donald, released it on HL-Inside forums back in September 2004, even before Half-Life 2 was released. It’s not Half-Life 2 story line related at all. There are 4 maps in this mod, where you will have to fight different enemies and at the end, you will meet The Thing.

Playthrough
https://www.youtube.com/watch?v=6BZ2UKhhXMU