There are many kinds of typhons that you’ll encounter in Prey, and most of them would like nothing more than to kill you. But there’s only one that exists solely to kill you. On your way into the Arboretum during "Detour," you’ll catch your first glimpse of a typhon nightmare. If you’re lucky, you won’t see one again for a while.
Update: After many more hours of playing Prey, we’ve updated this story with some better (and less panicked, frankly) advice about fighting nightmares.
WHEN TO EXPECT A NIGHTMARE
There’s no real way to guess when you’ll run into a nightmare. You’ll start to encounter them either after you complete the "Detour" objective or when you’ve chosen three typhon power neuromods. They spawn randomly after you go through a load screen, so there’s no guarantee about where you’ll meet them, either.
Nightmares do have a spawning cool-down period, which is a blessing. When you successful evade one during the "The Nightmare is Hunting You" objective (more on that below), they’ll disappear for 20 minutes. If you manage to kill one, that cool-down will last 30 minutes.
THE NIGHTMARE IS HUNTING YOU
When you first catch the attention of a nightmare, you’ll get a new objective named "The Nightmare is Hunting You." This gives you three minutes to either kill or escape from the nightmare. You even get a helpful countdown clock on your Prey HUD.
The surest way to escape a nightmare is to hit a load screen. If you’re not near a door that leads to a load screen (or if the nightmare is between you and the door), you can still just try to elude it for three minutes. Get somewhere out of sight, preferably somewhere you can lock the door behind you. Find an air vent or an elevator.
You may have noticed that we’re really focusing on the evade the Nightmare part of this objective, rather than the kill the Nightmare part. That’s because you can run away from a nightmare at any point, but killing one takes a little bit of planning.
FIGHTING A NIGHTMARE
Our first advice about fighting nightmares is: Don’t — you should run away, at least the first couple times you see one. It’s not going to be long before you are capable of taking on a nightmare, but no matter how far into Prey you are, a nightmare is still capable of killing you with one hit. That just means you have to be prepared and plan your fight.
Nightmares aren’t vulnerable to much, but nullwave transmitters and the typhon ability psychoshock will knock out some of its offensive capabilities briefly. And that will give you the advantage when you pick a fight with something called a nightmare.
The surest way to kill a nightmare is to hit it with a nullwave transmitter and follow that up with two or three recycler charges — the nullwave will keep it from from fighting back while you’re waiting for the recyclers to go off.
If you don’t have recycler charges, try to catch the nightmare unaware (the sneak attack bonus will help a lot). Then fire up combat focus and select your strongest (or, more accurately, the most damage per clip) weapon — it’s entirely possible to take out a nightmare with an upgraded pistol in this way.
One final note: Don’t trust the q-beam here. There’s a good chance the nightmare won’t be dead after your first full clip, and an even better chance you’ll be dead before you manage to reload.