Let's compile errors we have found in Mordenkainen's Tome of Foes

[the Jester]

Maybe I just skipped past it, but I think they forgot to include magic resistance in the stat blocks of some of the lower level demons.

Pretty sure that's a design choice, not an error.

 

[MechaTarrasque]

Pretty sure that's a design choice, not an error.

Maybe. The stat blocks were pretty full, so I figured they just ran out of space....

It seems a little funny that quasits have magic resistance, but (slightly) more powerful demons don't. Not a big deal, especially if the party has run into other demons and the casters are leery of direct casting at the demons.

 

[kbrakke]

The asterisk is referring to the Arcana Domain, which is in SCAG.

 

[the Jester]

Maybe. The stat blocks were pretty full, so I figured they just ran out of space....

That seems like it would be a major oversight, easily fixed by a small formatting change. I see no reason to assume this.

It seems a little funny that quasits have magic resistance, but (slightly) more powerful demons don't. Not a big deal, especially if the party has run into other demons and the casters are leery of direct casting at the demons.

Demons have never been especially consistent, which is perfectly appropriate given their chaotic nature.

 

[bkwrm79]

Are the Shadar-Kai supposed to have been nerfed quite so hard compared to the UA version? I'm wondering, especially when comparing them with the Eladrin, whether changing BotRQ to long rest instead of long or short is just down to missing words. Certainly I'd never play a Shadar-Kai exactly as written in Mordenkainen's.

(They also removed the bonus cantrip, postponed the post-teleport resistance to level 3, and switched the stat boost to Con, which could all be reasonable tweaks.)