Quote Originally Posted by upho View Post
As a sidenote, again I find Orcus' CR 35, not to mention the certainty expressed by the author whenever referring to the power of Orcus as written, not just sadly comical and embarrassing, but also a bit confusing.
To be fair, there are a couple of abilities that Orcus as written has in all his forms that can be seen as pumping his effective CR a pretty fair bit, depending on the DM’s proclivity for doing so to the hilt, especially the second:

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1). Summoning demons — this shouldn’t necessarily be unexpected, but adding up to 3 balors or around 7 mariliths (specifically atop the mariliths already present) isn’t nothing, but more to the point

2) Summoning undead — Orcus can summon 100HD of any undead (including, specifically, templated undead). If Orcus has any idea what the party is or does he can tune this ability — depending on the party’s composition, mobbing them with shadows might not actually be terrible, but book-diving and designing Orcus’ summons, yikes — “even” 4 semi-optimized 20th level liches should be, to put it mildly, a real problem. (Also, recall that all undead in the Boss Fight room, including the prestocked rabble, are fiat unturnable, and presumably could share Orcus’s and each other’s buffs.)

Given that summoned monsters in principle don’t add to the EL of an encounter because they are supposed to be accounted for in the CR of the summoner... Orcus’s summons alone could be 3x CR 20, 4xCR 22, or around EL 27 not counting environmental buffs for the level or room. It’s debatable whether that pushes Orcus all the way to CR 35, but it presumably establishes a bit of a floor as to his “actual” CR, and means this is one BBEG fight where action economy is not necessarily on the PCs’ side — Orcus summons can each have actions that are meaningful threats vs PCs, never mind that PCs looking to even the odds with battlefield control may find Orcus-liches, never mind Orcus himself, battlefield controlling right back at them.

Also note that Orcus should almost certainly have time to do his summoning before the Big Fight, and arguably should know *something* about the PCs even at bare minimum from demons’ encounters with them on this level.