Tomb robbers bring friends or associates with them to help haul away the treasure that they seek. There is safety in numbers, but it also introduces certain group dynamics—exploitable group dynamics such as friendship, caring, trust, and a variety of other deadly virtues.
You are on the southern threshold of a diamond-shaped room. At each point of the diamond, a 10-foot-wide exit leads away to destinations unknown. Each side of the diamond is 40 feet long.
The stunning switch trap activates only when more than one intruder enters the diamond-shaped room. The last person to enter the room within a period of time is the target of the trap. (GMs, adjudicate this as you wish.) He or she is first hit by a power word stun and immediately thereafter is the target of a variant mislead spell. The target becomes invisible, and an illusion of the target sprints toward the eastern exit, spouting gibberish along the way, then vanishes into the corridor.
Stunning Switch Trap CR 10
Type magical; Perception DC 33; Disable Device DC 33
Trigger sight (true seeing); Reset automatic
Effect spell effect (power word stun)
Effect spell effect (variant of mislead, DC 19 Will save to disbelieve)
Call for initiative. Brave party members will undoubtedly follow their companion into the eastern corridor to save him or her from apparent madness. You can spring a variety of traps on those brave, pursuing souls. On the edge of the eastern threshold you can place a camouflaged spiked pit trap.
Camouflaged Spiked Pit Trap CR 8
Type mechanical; Perception DC 25; Disable Device DC 20
Trigger location; Reset manual
Effect 50-ft.-deep pit (5d6 falling damage); pit spikes (Atk +15 melee, 1d4 spikes per target for 1d6+5 damage each); DC 20 Reflex avoids; multiple targets (all targets in a 10-ft.-square area)
Or to make things slightly more interesting, you can spring a cagefight on them. After entering the eastern corridor, a portcullis drops in front and also behind the unfortunate trespasser. One round later, 1d3 girallons are summoned into the impromptu cage.
Cagefight Trap CR 7
Type mechanical and magical; Perception DC 31; Disable Device DC 31
Trigger location; Reset none
Effect two portcullises drop to create a 10-foot wide and 40-foot long section
Effect spell effect (summon nature’s ally VI, summons 1d3 girallons)