Callista Ming's machine thing is actually Essence Transfer.
Midi-chlorian manipulation only has about three users, so it's definitely worth mentioning.
Flow-walking has more, but it's still very rare. That reminds me of Force-walking, which I believe is a very rare technique.
Shatterpoint isn't exactly common, but there's like ten known practitioners, so that's not exactly one of the most esoteric powers we've ever seen.
Dark Transfer only has two or three users as well. That needs to be mentioned.