Azrael Nightstar
First Post
I was thinking of this partly (or even primarily) as a roleplay-oriented tactic, and of course its success on that account depends on your group. The "unpleasantness factor" wouldn't bear much on the players, but the characters wouldn't want to arrive on a new plane every few hours feeling like they'd just been worked over with a 9 iron (to use the "travel is painful" example). Also, don't forget about the various other ways to make it unpleasant for the characters, assuming this sort of thing will work with your players. If not, it's probably not a good option (on that note, see below re: carborundum's suggestion)
I was actually thinking MUCH lower if it's a flat chance, so that Bob the Fighter can be told "there's a risk to it, but it's very low. Well worth it for our cause, don't you think?" The risk could be further diminished if it applies per portal rather than per traveller; if poor Bob finds himself in the 475th Abyss, he can at least be reassured the PCs and the other travellers will be there too, and they'll all get back together.
I'd also suggest much lower if it's a cumulative chance, say 1 in 1000 to start, but make the growth exponential. The 2nd trip the PCs make to the Caretaker's realm their chances are 2/1000, then 4, 8, 16, 32... This makes travelling to the plane more than absolutely necessary VERY unappealing after only a handful of trips, but for the henchman only making 3 or 4 translations, the chance is pretty miniscule.
Another option with this method is to set a threshold. No risk at all until you've gone back and forth 3 times; then you're taking your life in your hands. No risk at all for the new hire, but the PCs have a real good reason to limit themselves.
Certainly the simplest, but I put it last for just that reason; heavy-handed NPCs are sometimes a necessary evil, sometimes appropriate and fitting, sometimes both. In this case, where you don't really have a specific reason to use that mechanic, my advice would be to avoid it. Better to not properly re-enforce the theme than to overdo it. The players might enjoy the change of pace anyway.
Meant to mention that, another trick is that if you go with just straight charges, make the number unknown (and undiscoverable). You can give the players a vague idea so they know that they don't have to wait until they've gathered 200 men to march through at once, but the doubt is likely to give them pause about frivolous trips. Another bonus here is once it's all over, they can use up the rest of the charges for whatever they want. The item could become as you mentioned a quick escape route, or maybe the favorite R&R spot?
This is a good one, its simple and elegant in that it directly addresses your stated concern, and little if anything else. This would work well coupled with the "unpleasant by exhaustion" idea. You can really impress upon the PCs that not only do they feel wiped out, but whatever time they've gained is lost to them (and then some, if you go 12 or 24!)
A variant on this concept would be directly affecting the benefits of rest. Don't allow the PCs to heal on the demiplane (healing such powerful beings is overly taxing on the Caretaker's resources), memorize spells (the mind-bending jaunt through a tear in the fabric of reality does a real number on casters), etc. Mix and match as you see fit if you want to allow them SOME of the benefits.
A variant on THAT is that the trip itself negates the benefits (you take damage, suffer spell drain, etc.) You can rest up if you want, but you'll just be injured and drained when you get back anyway, so what's the point?
The only downside to these is they don't really address the item's use as a "handy escape plan", if that's a concern, but that's remedied easily enough: Make the casting time too long for this to be viable, or require a relatively calm environment for casting. You could require a Concentration check with a hefty penalty; if the PCs get in it awfully deep they can still try, the drama palpable as the wizard tries and fails round after round while the others try to hold the line.
Stipulating that the journey inflicts damage could also put a kibosh on any designs to escape at will, if the damage inflicted is high enough. If they're in deep enough to want to turn tail, chances are good someone won't survive the trip.
