Up To Their Waists In Demons

[Oriande]

I am somewhat worried about the threat posed by the next story arc I have planned. I currently have six PCs at "Up To Your Waist" i.e. 25 skill points, skill cap - great, and base refresh of 7.  I am planning to pit them againt a demon similar to Kalshazzak, the "toad demon" from Stormfront, but I am worried that this might be too much for them to handle.
I have done the calculations for a mixed group from Scaling the Opposition in YS and the creature comes out as Challenging which sounds like what I have in mind, but I am still concerned.  
This is a realitively new group of characters, and all of us are new to the FATE system. So far they have defeated and destroyed a WCV who was newly arrived and a handful of his minions.  By the end, one PC was hospitalized, several were injured, and one was suffering from a moderate case of depression.
Again, this seems reasonable, especially considering that the player of the hospitalized character [He had his guts ripped out by a ghoul.] refused to use either concessions of fate pionts to avoid or mitigate that outcome.
So, am I worrying too much?  What sort of threats should they be able to handle, and how much damage is it fair to do to them in the process?

[luminos]

This isn't the most helpful answer, but the appropriate level of challenge is highly dependent on what the PC's are playing.  If there are a few pure mortals in the group, then a kalshazzak level opponent will be a difficult challenge.  If the PC's all have channeling and/or maxed out combat stats, they should be able bulldoze Kalshazzak without taking very many consequences. 

I think that from what you described of their earlier combat encounter, a kalshazzak opponent should be just right.  He'll be a challenge, and require either a bit of strategy or luck, but it won't seem impossible.

[Lanir]

It sounds like the concern is not so much how the mechanics stack up as it is how well the players will use what capabilities they have. That's a good thing for a GM to keep in mind. One of the best ways to handle this is to have a contingency or three in mind. Which can involve backup arriving, the demon getting weird orders (bad guy has a crush on one of the characters so orders demon not to hurt him/her, or the fight is in a museum the bad guy doesn't want messed up, etc), the demon stopping to munch on bystanders, or even a combat in a weak structure that's falling apart. Any decent sized blast or the demon throwing a PC through a wall or whatever results in a partial collapse that blocks the good guys and bad guys off from each other. The demon has forever so it's not in a rush.

[HumAnnoyd]

Contingency plans are the best way to deal with a situation like this. I was running a Lord of the Rings campaign a few years back and faced a similar problem when confronting my party with a Troll.  My PCs weren't all that powerful at that point and were pretty much getting their ass handed to them.  I realized that I had miscalculated how powerful the Troll was and was relieved when the Dwarf in the party spent a Drama Point to collapse the tower that the battle took place in on the beast's head.  Otherwise the encounter would have resulted in a TPK.  I am lucky my players were so innovative and after that I made it a point to have an out just in case when the group faced powerful opponents. 

[Becq]

You might also want to look over the suggestions in "Adjusting Opposition on the Fly" (YS336-338).  It gives some useful thoughts involving fudging the power level of the NPC on the fly, as well as thoughts on how to make use of Concession to make it so that even a complete party wipe need not be the end of the world.

[Haru]

You could always plot-devise him to death, but in my experience, players get used to that and start slacking on their preparation for a big fight. However, if you feel you underestimated the demons power, you can always make him disappear, maybe because the sun is coming up, any kind of magical threshhold would work. If on the other hand you feel your players are not well enough prepared to confront the demon, tell them, maybe directly out-of-character, maybe more subtle through a contact. When they finally fight it, they should be well prepared. And they outnumber it 6:1, I think they have a good enough shot at it.