Half-Life Walkthrough

The entity behind all of this chaos and strife turns out to be a really big alien baby. You'll be dropped into a big cylindrical room with Nihilanth floating in the middle.

Use the spikes sticking out of the floor to your advantage! You do not want to be hit by the blue balls that Nihilanth throws, but the green balls are worse -- they home in on you, making them impossible to dodge, and they teleport you to secondary rooms where you have to hop up platfoms or bouncy craters to make your way through another teleport back to the action. Whenever you think the big baby is about to toss a green ball, block its path by hiding behind the spikes until the danger is gone.

To weaken Nihilanth, you need to destroy the 3 green-crystal triangles which are high up on the walls of the room. The easiest way (at least for me) was to turn off the red dot on the RPG, aim carefully, and quickly take all three out.

Little-known fact: the material that makes up the three green triangles protecting Nihilanth is the same as the crystal sample which you pushed into the beams to start this whole mess in the first place. Valve Software originally intended to make this connection more obvious but never did.

Once all three green triangles are destroyed, Nihilanth is ready to have his ass kicked. Take the bouncy craters to vault yourself up above his now-opened skull, and unload the strongest weapons you have into his exposed brain. MP5, egon, shotgun, whatever you have will work; you can even toss in snarks or detpacks, and the true warriors will pith Nihilanth's brain using the crowbar.

Once Nihilanth bites the dust, watch the fireworks and then prepare yourself for the final confrontation. Choose whatever path you decide suits you best.