I have been playing with an idea for a plot device.
Imagine the characters have the bad guys fighting a tactical withdrawal. They are falling back slamming and locking doors with the intention of slowing the characters down.
This presupposes that the bad guys have something that the characters need.
Lock and Magic Lock are 1st and 2nd level spells, Opening I is 4th level (based upon the RMu beta Spell Law), so the doors are a powerpoint drain on the party, more so than on the retreating bad guys.
At the end of the chase, or the top of the tower, is a small plinth, that the characters get to see the villain step on to and disappear. Not a subtle winking out, but with your best sci-fi shockwave and thunderclap, to accompany the disappearance.
The plinth glows slightly and this takes two or three rounds to fade, and then another minion steps on to the plinth and disappears. The glow and fade process happens again, and then a third minion disappears.
So by now the characters should have the idea that this only works on every third round, or it takes two rounds to cool off and reset.
Whatever the characters needed are on the other side of this teleport portal.
Do the characters follow?
This is the first dilemma. If they are going to follow the villain into their lair, they need to go one at a time.
You can bet your bottom dollar that appearing at the other end is not going to be any more subtle than disappearing was. Going in visible and trying to sneak through is not going to work here!
They will also be facing every bad guy that went through, vs just the first character to arrive, and then the next.
But why build a portal that works so slowly? How about one that leaves a character disoriented on arrival. Anyone arriving is stunned for a round by the concussion caused by their arrival. The time lock allowed for this and for the person to get clear before anyone else teleported in.
If you can get three or four bad guys through the portal before the characters take control of it, you have odds of four to one against, and the one is stunned for at least the first round.
You can also assume that the last bad guy through will have told the others the state of the battle they left behind. The bad guys will know when the next person through will not be friendly.
What parties and players thrive on is working together as an elite team. They take on odds that they should never survive.
This challenge will test them, as individuals, as pairs and then as smal teams. It almost feels like those puzzles when you have to get a wolf, a chicken and sack of grain across a river.
Does a fighter go first, to create a foothold, and let the others go first? But a fighter vs. a well prepared spell caster rarely bodes well for the fighter. When do you send the healer through? After 3 rounds or 6? The magician would be a good idea to go higher up the batting order, especially as there is no longer a need to prep, but how many power points will they have left if they have been unlocking or blasting their way through doors?
Where did Everyone Go?
If we just teleported everyone somewhere, where did we put them? And does it matter?
Imagine you had nearly unlimited time and either Gate Mastery or Earth Law. The gate master could summon and hopefully control an elemental at 6th level, without overcasting. Grade I elementals are not too useful but a Grade II can turn rock to earth (which is easier to excavate) and generally throw Earth Law spells around at up to 9th level. If you have Earth Law you can do this yourself.
With an earth elemental you can start building your Bond Villain base.
I am talking about teleporting the characters inside a mountain or even straight down. The only real need would be for some kind of ventilation, for air.
You can now put your somewhat depleted characters through a dungeon crawl. If the bad guy had kept some rune paper down here and made a supply of summoning/gate type spells. They can throw disposable monsters at the characters. The bad guy could also get a message out, and bring more minions, agents or even mercenaries through the same portal to bring in ever more foes.
The teleport portal is of course one way, and somehere down here is its twin, that gets you out again.
The characters now need to find the villain, retrieve whatever it was that they needed, and then find the portal to get out, whilst fighting all the nasties that you can throw at them.
Going out, resting up, and coming back for more is not an option.