Does a Monstrous Humanoid or a Fey count as Humanoid for armor costs and spell effects?

Question

A question for two friends playing custom made races. One is a Monstrous Humanoid physically similar to a Lamia but with a larger bust and a less ridiculously long snake tail, the other is a Fey of humanoid shape with wings. Both wear armor, the Monstrous Humanoid is combat-oriented with a bit of spellcasting, the Fey is mainly a spellcaster.

First, is there a general rule about a Monstrous Humanoid or Fey being considered Humanoid or not to determine the price of armors, or is it solved on a case-by-case basis ? And how would it apply in my particular case ?

Second, do spells and other magical effects affecting only Humanoids work on Monstrous Humanoids or Feys ?

Answer 1

Equipment

In the section on Armor for Unusual Creatures, it breaks it down into humanoid vs non-humanoid, but as we can generally see from creatures like centaurs and driders, they have a trait called "undersized weapons" which allow them to use weapons as fit for a medium humanoid. Most GMs I've seen (including me) have said that if the creature wears armor, its fit for a medium-sized humanoid as well. This isn't backed up in RAW as far as I can tell, but it isn't far out of the realm of possibility.

I'd see the armor section as more of a body-type rather than race-type classification. This also covers more "standard" races that are non-humanoid, like Aasimar and Tiefling.

Spells

Spells explicitly targeting a type of creature go by race-type, not body-type. So they are playing with the same restrictions as any race with the "outsider" type, such as Aasimar and Tiefling, in that spells that target humanoids do not work on them. For instance Enlarge/Reduce Person will not change their size, but on the flipside Charm Person also has no effect on them.

Answer 2

In a case like armor and weapons, it is more useful to use "humanoid" as a descriptive term, rather than referring to the specific creature type. Going by a descriptive method, it's easy to classify many creatures as humanoid: anything with 2 arms, 2 legs, a torso and head.

However, when faced with a creature with non-standard anatomy, such as wings, extra arms, serpentine or equine lower half, and so on, you are definitely stepping outside the regular "humanoid" shape, and they would need customized armor to accommodate this. Normal humanoid armor simply would not cover them appropriately.

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When referring to spell effects, this is a much more specific matter. When a spell specifies a target as a certain type (humanoid, monstrous humanoid, fey, undead, etc) it means only and exactly that type (or those types, if multiple are specified).

A fey creature that is visibly indistinguishable from a humanoid creature is nonetheless not the same type of creature for handling spell effects.