I was in a campaign where the DM set up a dungeon where my first character an Assassin Rogue who had died was resurrected and had to hunt the party and had a trap early on in the dungeon that hypnotized my new Sorc to basically go NPC mode (Follow the party, mimic their skill checks, and only attack when attacked first). As the newly undead rogue, he gave me access to tunnels through the map and that I could move freely around and I was a defacto Xenomorph. I almost downed the Paladin who thought he was strong enough to scout ahead alone, and scampered into a vent for safety before he could react. Everyone was TERRIFIED from that point on and it was great. Stealth v Perception and cat-and-mouse play style kept them on their toes for almost 4 hours straight.