Candidate Twelve is a BMS remake of Half-Life: Echoes, another Half-Life mod created by "Mr. Gnang". An unnamed scientist referred to as “Candidate Twelve” is forced to survive through the facility as they face unknown alien danger, while being stalked by two opposing interdimensional entities.
A tidbit from S4.
Should make it where the construction worker is running from a headcrab which is the reason why he would run into a barnacle, and you would have to lead the headcrab into the barnacle.