Hi y'all. I'm writing my own module and I've got some ideas for encounters that I'm very excited about. The only downside is that they're too high CR in the end! The section I'm currently working on is a keep called Grasswall. The PCs have infiltrated the keep by this point, and are facing a gnoll with 7 levels of cleric who has been built up throughout the module. That's a CR 7 encounter. The PCs are 5th level here, so it's boss-level. I was planning on adding some support for the cleric, as solo casters tend to melt like ice in Death Valley against a party of PCs, and was thinking of adding a weakened unique chimera (CR 6) for his mount. He'd be initially fought in a ritual chamber in the keep itself, then he'll meld into stone (if possible) once he's damaged enough and move up the tower to mount his chimera and fight the PCs there.
The downside is that the CR of these encounters will be all over the place. A CR 7 cleric with a couple of acolytes (probably inquisitors or fighters) will be at least party level plus 3. I dislike the CR system overall (it seems arbitrary and not the greatest of guidelines at times), and since I'm not using xp in this module, it won't affect the PCs' level. I'm just worried that I'll inadvertently cause a TPK. Does anyone have some experience with this kind of thing? Maybe some encounters that should have been hard but were easy, or vice versa? Any advice you can give me will be appreciated.
The cleric isn't the final boss of the module, or even the keep- that's a CR 10/MR 1 mothman and a CR 7 dragon, respectively. He's just been built up a lot, and I want to make this memorable.