Half-Life Opposing Force-Worlds Collide

After making his way through warehouses filled with Race X creatures and Black Ops fighting while finding another way out, Adrian Shephard arrives at an old industrial area of Black Mesa deep underground where the enormous Gene Worm is attempting to come through a portal from the Race X homeworld. Shephard uses mounted laser weapons to blind and kill it; in its death throes, an enormous teleportation portal spreads outwards and envelops him.