Hiya.
I guess I'll be the voice of the Great Curmudgeonly Grognard...
Eh? Whats that? Encounter CR budget? What in carnations is that? ...ehhh....never mind. Probably one of those new-fangled mathmaticaly-type doo-dad rules some young whippersnapper came up with to make himself feel better about lettin' a whole party o' 12th level PC's die when they up n' run inta'a demi-lich in it's lair or sum'mn'.
Yeah, back in my day...er, wait...I still do this to this day so can I even say "
back in my day"? Anyway, I've never used any formula, CR math, or XP budget for my games. I'm a DM who "builds" encounters without regards to the PC's well-being other than a general "this is their level, so I'll keep things about their level". In other words, I wouldn't put a demilich in a cave for their 12th level PC's to fight. Too much of a difference.
That said...IF the party heard of "Oh, don't go to the Cave of Whispers! The long-dead lich Mogg was slain a decade hence, but everyone says his evil was so great, and his desire for power so consuming that his
head still haunts his lair!"... and they still choose to go get 'em? Well, in the immortal words of one E.Gary Gygax, I "
Let the chips fall where they may".
So, if they, as a group, have knowledge or at least serious contention that a demi-lich is there...go ahead and build away. I'd go with the demi-lich, one vampire "aid", and perhaps a pair of sexy female ghoul twins just to spice things up a bit. Would I be worried about a TPK? Nope. Not my job to worry about a TPK...that's the players job. If I say "You open the door, revealing a 40' square room with a 30' heigh ceiling. The far wall has a 5' wide ledge up at about the 20' mark. On that ledge you can see a pedestal with an old, purple, velvet pillow with gold tassels on the corner. On top of it sits what looks like a mummified head with gems for eyes and teeth. All along the ledge on either side of it is treasure, almost spilling over onto the ground. On the ground directly below it is an ornate coffin. To either side of the coffin, two obviously female ghouls slowly rise to their feet and smile at you. As one they speak, 'Our masters have been waiting for you...'.; ...so, what do you guys do?".
If the party replies with "We attack!", then I've done my job as DM and wash my hands of any responsibility for the outcome.
Conclusion: Play it by ear and base it on internal campaign logic and consistency FIRST; PC capabilities come a fairly distant SECOND. Use your knowledge of your players PC's overall toughness and set that for your 'gut-feeling foundation' for creating your adventures...but don't be afraid to put something significantly tougher or weaker against them, as long as they have reasonable suspecian about that tougher/weaker encounter.
The whole CR thing starts to break down (rather quickly!) the moment your PC's start to fall outside the norm upon which it is all based. For example, if your PC's have magic items...the CR creaks a bit; you are using Feats in your game...the CR groans noticeable; your players party makeup is two paladins, a druid and an edritch knight...the CR visibly cracks in multiple places. Now, toss in a group of players that work well together and are adept at tactics "outside the box" (like being really good at using normal equipment and terrain together to gain a significant advantage over their foes), and ker-BLAMMO! The CR system is now mostly moot. So you definitly have to take the "overall level" (character level, player level, power level, etc) of your group and use that as a base; just trying to go by the numbers will work less and less the more and more your players and their PC's fall outside the "norm" upon which the CR system is designed.
For the record...virtually every single game I've ever played has had a group that is falling "outside the norm"; some only slightly, some vastly. This has taught me one thing: the CR "system" for building an encounter is only remotely useful as a "baseline generalization". If it takes you ten minutes to whip out your calculator and do a bunch of math to figure out the 'correct power level' of an encounter, and at the end of it you are thinking "Hmmm...that doesn't see right..."...then chances are
it isn't right!
My suggestion for your situation? Add more zombies and skeletons, but make sure the Players
can find out that "the demilich is guarded by a dozen or more skeletons and zombies!". Notice I said
can find out and not
do find out? Yeah, if the Players just rush into things like fighting a demilich and his undead retinue when they are only 12th level...well, IMHO, there are no stupid players with 20th level PC's for a reason.
(or at least, there shouldn't be...*sigh*... ).
^_^
Paul L. Ming