The original and maybe the only trailer made for Gearbox’s Half-Life: Opposing Force.

Half-Life: Opposing Force is one of the expansion packs for the original Half-Life. It was developed by Gearbox Software and was published by Sierra on November 1st, 1999. The story follows Adrian Shephard, a corporal from the Hazardous Environment Combat Unit that has been called to silence the Black Mesa Research Facility and clean up the mess caused by the Resonance Cascade.