Here's another thought for a situation:
A locked etherstone (stone fully present on both the material and ethereal plane and thus not susceptible to blink, etc) chest in a treasure room. It is, of course, trapped. (DC 34 search/Disable Mordenkeinen's Disjunction trap). Inside is a very attractive looking widget. Perhaps something that looks like a robe of the archmagi or a +5 subtle dagger of venom--something very tempting. Of course, the inside is also trapped (again DC 34 search/disable trap; this time, however, it's a Meteor Swarm/Power Word (up to four targets in all of whom must be in the room kill trap. The meteor swarm goes off first, of course).
Alternatively, you could have the liberators stumble into a breeding ground for Iuz's undead minions. The Liberators open a door. Inside, it is dark and there are nothing but bodies covering the floor in various states of decay. They all look like they died a horrible death. Stepping in (because dead bodies often hold loot), the liberators discover that this is where Iuz pitches prisoners he has no more use for. They are slain by some kind of (preferably high HD incorporeal stat or level draining) undead creature that creates spawn. Whenever Iuz's priests need a few undead minions for a scheme, they cast Death Ward, go in there, command a few of the undead and leave. Whenever the stock runs low, they toss in a few prisoners or failed minions.
Of course, this is where the trick comes in. Whoever was in here last used an anti-magic shell causing all of the undead to wink out of existence. When the PCs enter the shell, it fails and all of the undead pop back into existence surrounding them. Alternatively, you could have a villain in here apparently waiting for the liberators to kill the S--- out of him in his anti-magic field. When the liberators close to melee with him, he dismisses the anti-magic field and all of his undead hordes pop into existence around the liberators. And, to add insult to injury, after dismissing the anti-magic field, he uses a quickened dimension door to escape. Bonus points if it's not even really him but just a projected image or simacrulum. Double bonus points if he cast mass resist energy on the undead before hiding them and is standing next to a brazier of fire. After dropping the anti-magic shell, he drops (free action) the entirely unused necklace of fireballs that he has in his hand into the brazier and dimension doors away before it lands and all of the beads detonate. For the triple bonus score, he could have developed a special heightened, energy admixed necklace of fireballs that does more damage and does damage in different energy types. And you hit the jackpot if he's used Imbue with Spell Ability to give his familiar the ability to cast Greater Dispelling and handed a metamagic rod of chain spell to his familiar.
So the whole sequence goes like this: Liberators move into the room to kill the villain. Villain dismisses the anti-magic field, the undead pop into view surrounding the liberators, then his familiar targets the liberators with a chained greater dispelling hitting each of the liberators AND each of their obviously magic items, then his familiar hits one of the Liberators (probably Heydricus) with a quickened ray of exhaustion, then he drops the necklace and quickened dimension door's away (sharing the spell with his familiar) then the necklace lands and all the fireballs explode.
Ouch!