You might want to leave the lights on after this one... As you and the BOBs return to the Sol system, you come across the ruins of an ancient society - though you shortly find out that the ruins aren't completely abandoned. Discovering advanced technology, you and your shipmates discover a race even more powerful than the S'pht'Kr, and with a secret just as deadly. To prevent the end of the universe, you must find their secret, and still make it back in time for a good cup of coffee.

Becuase of several new enemies and new weapons, many of the same tricks that worked for Marathon or its sequels fail to work here. Be warned.

Regarding weapons...

• The Pfhor staff is probably your second best friend in this game, after the plasma pistol. Besides having an unlimited ammo supply, it works great when you can trap monsters in tight corridors or one-on-one situations. (Especially the Mystics!) It also lets you trigger switches similar to grenades and the like.
• The rail gun is quite powerful as well, but don't use it in close quarters! If the rail gun impacts with something close to you, you'll take severe damage. The rail gun can toggle switches as well.
• Same can be said about the nuke packet gun. Use only at a distance. Being near the blast radius for this weapon can take away up to two shields, if not more.

Regarding monsters...

• The Devlins like to rush and pierce you with their talons. Your best defense against them seems to be the shotguns, though any of your weapons will work. Give yourself enough space to back up and fire.
• The Mystics are similar to the S'pht, but they lack a few powers that the S'pht had (such as flying), while gaining a bit of power with their energy bolts that can follow you. They are best taken out close up (watch out for their death explosions) using the Pfhor staff, but other weapons can work equally well.
• The new drones come in several flavors - grey drones are on your side, reddish-brown drones will fire at you, and the green drones will try to explode in your face (a la explode-a-Bobs). All three, when they die, will have a small blast radius, which can be useful and deadly.

Saving ammo on in this scenario is key. There is just enough to finish the game with what is made available, but you will have to rely on the Pfhor staff many times to keep your ammo supply up.

Make sure that you recharge and save often, even if it means navigating a tough section of the map (sans monsters, of course). There aren't many of these terms, so use them as much as possible.