I was thinking of some super PCs, like centaurs and monster PCs, and I remembered the 4/6 armed Humanoids as an interesting addition. The most popular ones I'm aware of in mythology are Deva, but D&D has lumped them together as Angels.

I know there's a Marilith, I'm curious what other prominent multi armed creatures the game has, and why Deva aren't one of them 🤔

Deva is a generic term for celestial beings like the term angel is, so I do not see anything wrong with devas being lumped in with angels. Asking why devas do not have multiple arms is like asking why angels are not depicted as wheels covered in eyeballs. Some individual or minor subcategories of devas have multiple arms, but the vast majority do not. Ophanim are a type of angels covered in eyeballs and are also sometimes depicted as wheels covered in eyeballs, but most angels are not covered in eyeballs and definitely do not look like wheels.

Devas also vary by region and religion, but they are generally not very different from regular humans in appearance.

To clarify, in Dungeons and Dragons 5e, as far as the Monster Manual is concerned, a Deva is a celestial being, and one of the three _types_ of Angels available in that book.  It's not a generic term but rather denotes specifically the MM angel with the lowest challenge rating of the three.  

Across a range of intersecting as well as distinct IRL mythologies, religions, and spiritual practices, the word deva is used to name a variety of "higher beings" or "spiritual forces."  I wouldn't call that a generic term however.  In some case you may have the word coming from similar Sanskrit origins for instance, in others you might have attempts to reverse engineer Latin notion of divinity to Sanskrit, etc.  

I'm not sure where specifically the multi armed Deva the OP is trying to reference is from.  There are multiarmed deva depicted in some Hindu referencing imagery; but I don't know if they're trying to speak to that or some "western" angel (and there you got distinctions between christian apocrypha and New Age stuff, among others) where sure, sometimes they're presented as having two arms, they also aren't.  

Quote from Bahamut_Kaiser >>

I was thinking of some super PCs, like centaurs and monster PCs, and I remembered the 4/6 armed Humanoids as an interesting addition.

 I'm not clear on what exactly you mean here, but if you're asking why there's not a PC race with extra arms it's probably because that would be super strong. Simic Hybrids can get extra limbs, but they can only attack/grapple with them. If we ever see Thri-kreen, they will likely have extra arms as well but also with restrictions as they typically aren't as strong as the primary arms.

It's a pretty hard thing to balance, as something swinging a greatsword with a shield while another hand is tossing around components is breaking multiple baked-in character limitations. Even if we saw Deva in 5e, don't get your hopes up - they only had two arms in 4e.

🤦‍♂️🤦‍♂️🤦‍♂️

More importantly where are donuts made of eyes and divine lame, bending time and space with their very words? Old Testament have some METAL angels in it, things that would cause sanity checks in other systems, but we commonly only see boring winged humanoids and cherubim.

Quote from Mezmerro >>

More importantly where are donuts made of eyes and divine lame, bending time and space with their very words? Old Testament have some METAL angels in it, things that would cause sanity checks in other systems, but we commonly only see boring winged humanoids and cherubim.

PLOT HOOK: Celestials appearance are a facade masking entities from the Far Realm.  Maybe as a saving grace to the cosmology, the celestial appearance is like the Encounter Suits of the Vorlon in Babylon 5 (whose mythology I think supposed most species first encountered them as Angels or other higher being spiritual emissaries).