Prototypes

"I remember why I am not allowed down here anymore..." - Bubby

The Prototypes are hostile enemies seen in Act 4, clone-like creatures visually similar to Bubby, though with very obvious differences. Most of them likely cannot speak, assumingly cannot walk thanks to visibly crawling on the floor (with a few exceptions seen simply standing in the finale), and are immediately hostile in Gordon's presence, crawling towards him with animalistic growling noises and attacking him before he eventually kills them. They are holed up in a seemingly abandoned sector of Black Mesa, with broken light fixtures and closed-off portions of the hallway. Bubby implies that he was never given much info on the Prototypes, briefly mentioning in Act 2 that he only knows of their existence, and stating that he "isn't allowed down here" in Act 4 because of their failed experimentation.

The prototypes make a return in the finale as one of the groups of enemies guarding Bubby's Passport in Xen.

Trivia

 * The prototypes are scientist models used to replace the model of the Fast Zombie in Half-Life 2, specifically only the upper torso.
 * This is also the reason why they take so long to kill, since enemies in Half-Life 2 have a lot more health compared to those in the first game.
 * Additionally, their legs stick up in the air since the Fast Zombie torso does not have legs, so the Half-Life 1 models resort to their neutral position.
 * Bubby mentions in Act 2 that he had brothers growing similarly to him, referencing the prototypes.
 * However, Bubby has no further information at the time besides this, including the location at which they were grown, stating his "neurological implants" won't allow him to tell anyone.
 * In the finale, the AI of the prototypes is similar, however, they were given an obscene boost in health.
 * Wayne states that he originally intended the prototypes to be able to inject targets with various drugs, although this never came to fruition.