(I was actually heading this way for the SP map I'm working on, very few ennemies, but very deadly and scary).
F*CK, Yeah! Make the player suffer for taking on some ball busting AI. Wanna randomise that shit? Add a key framed object, let's call it 'X', or whatever. Set the key frames to loop around the level so the object passes above or below every location that the Player can get to. Set the commands on the AI, especially an Headbiting, wall walking alien to constantly roam the level: 'mt X' so it's trying to find that object that's moving around. Then tell the AI to 'mt Player'. Alternate these commands. I forget all the proper syntax but it can be done and you will have a free roaming AI that will wander the level looking for 'X' and then choosing to hunt the player. You'll need to set up some time delays in the command and multiple paths throughout the map with AI volumes but it creates a completely random experience for encountering the AI.
Just add one Alien. Light the map carefully, add some sound cues and don't give the Player any weapons and you WILL scare the shit out of them. lol.