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Orcus, the demon lord of undeath, is listed in Mordenkainen's Tome of Foes on page 152-153. He has several lair actions, including the following:
Orcus's voice booms throughout the lair. His utterance causes one creature of his choice to be subjected to power word kill (save DC 23). Orcus needn't see the creature, but he must be aware that the individual is in the lair.
Power Word Kill, however, states:
You utter a word of power that can compel one creature you can see within range to die instantly. If the creature you chose has 100 hit points or fewer, it dies. Otherwise, the spell has no effect.
There is no save DC, that's the whole point of the spell (which is 9th level).
Why is there a save DC given for Orcus' lair action? Is it for balancing purposes, so that players don't have to deal with a "you most likely die now" feature every round? Or could it be a mistake from the developers? It would clearly be too strong without a save, but even with that, a DC of 23 makes success unlikely if you're not proficient and naturally good with the relevant save ability (which is not given and therefore unknown).
I'm specifically interested if there are other features with similar issues, and if there are any rulings/statements from official sources about it*.
Of course, if the given DC is not a mistake, but rather intentional, it raises the question which ability to use for the saving throw. CON would make sense, but RAW, none is given.
* I'm aware that developer intent is considered off-topic for some time now. Feel free to answer this question without designer quotes, though I don't see how this issue could be resolved without insight from a designer. Still, maybe you'll discover something I missed :)