Great list
@Ash Mantle!
Sorry for the noob question here - but what is the difference between ethereal stride and plane shift? For instance could one create a home-brew Deva that could say have Celestial Flight (as opposed to 'stride'), or would it have to be plane shift? Not sure I understand the nuances.
Plane shift is a 7th level spell, which lets the caster transport themselves to any other plane of existence, as long as they have the right kind of material component (which needs to be attuned to the specific plane). The component isn't needed if the creature can cast it innately.
Ethereal Stride is a specific feature from the statblock of a nightmare, which makes this happen: "The nightmare and up to three willing creatures within 5 feet of it magically enter the Ethereal Plane from the Material Plane, or vice versa."
From a functional standpoint, the difference is this: the other can transport you onto any plane you specify while the other only enables travel between the Material and the Etheral Plane.
What one gives to a home-brewed Deva is entirely their call, but you should note that
plane shift is noticeably more powerful than
ethereal stride and probably raises the monster's CR.
If we're using the RAW versions of both
plane shift and
ethereal stride, I would argue
plane shift is the better fit. This is because Devas are from the (Lawful Good) Upper Planes, and copypasting Ethereal Stride word-for-word would be of little use to them, since it doesn't offer any way for them to visit their home plane.
If you would take Ethereal Stride and change the mention of the Ethereal Plane with Mount Arborea (for example), you would end up with a Deva who might be slightly more powerful than the one in MM, but not by much. And it's still loads tamer than a deva who can transport themselves onto ANY plane of existence in the Multiverse.
More about the Ethereal Plane and plane-travel in general can be found from Dungeon Master's Guide, Chapter 2.