A while back I had an idea for a group of villains for a D&D campaign, with the core idea being that each one was a different sort of shapeshifter. A Rakshasa, a Night Hag, an Ogre Mage, a were-creature, a Succubus, a Doppleganger, a Changeline, that sort of thing. I might give some or all of them them class levels (or at least the NPC equivalent of such), but insofar as possible I wanted them all to be natural shapeshifters in some form or other.

Anyway, with that in mind, I'm looking for inspiration with a few things:

1) Are there any other shapeshifters you'd recommend, either in 5e or from past editions?

2) The main thing I'm looking for is what sort of scheme(s) a group of shapeshifters might want to enact. I've had a couple of ideas of my own, but this forum has been a great source of devious ideas in the past so I thought I might as well ask. If it matters, I want the shapeshifters to be working towards the same ultimate goal, but they don't have to stay together all the time; working solo or in smaller groups is fine. They can also have non-shapeshifting followers and such, it's only the main villains that I want to be shapeshifters.

3) Potentially related to the above points, which shapeshifter do you think should be leading the group? I'd been inclined towards the Rakshasa but I'm open to alternatives.

4) Of course, if you have any other ideas or suggestions for this sort of thing, I'd be delighted to hear them.