Here's another take on vampire PCs. There are two versions; I recommend reading the newer one (v3.4).

What sort of abilities would a 5e playable vampire have?
Might go more for something like the UA Diplomat feat.I would give them friends cantrip and a once per long rest vampiric bite attack that does 1d6 piercing and gives you an extra hit die or the dmg done in temp hp.
Thanks!
This would definitively be a big no-no to put this class next to the monk: its more or less a cheap reskin
From my perspective, this would replace the monk. Why? Because I think that with the new generation of players, the ''kung-fu movie'' vibe of the monk is a little passé (at my table, at least). They have a 80' feel that we, as players born in the 90' and 2000', dont relate much. Anime and JRPG heroes are more trendy, and I believe that a Fighting Style that allows a fighter to have a competitive AC without any armor, a maybe some fighter archetypes using unarmed strikes or exotic weapon would fill the niche easily. Then, you replace the class with the Abomination, a class that satisfy the edgy/emo class niche that new players love so much.
About the Hit Die as a resource: I think the archetypes will use them. Vampire will have a bite attack X time per short rest to regain health by spending 1 of the target Hit Dice. Revived will spend HD to pass trough walls, Shifter will be able to spend HD when first shifting to gain a pool of Temp HP, Slayers will use their HD to lower lose some accumulated beast point etc.
I like itOk, well, I changed my mind. I think that reusing the ''discarded/unused'' UA Mystic's disciplines would lend better results.
- Remove unarmed attack progression. 1d8 natural weapons, +1d8 necrotic at 10th and 14th
- Remove movement bonus but keep unarmored defence.
- Psi point = Willpower
- No Talents, just Disciplines.
- Disciplines dont have ''focus'' bonus.
- Less Disciplines per PC
- Keep the UA Mystics as is for the rest, but design better archetypes.
- Trim the disciplines list, keeping only those that makes sense:
Aura sight, bestial form, brute strike, celerity, corosive metabolism, the 3 ''crowns of'', giant growth, iron durability, mantles of fury/fear/ awe, mastery of light and darkness, chameleon, psi weapon/restoration, psy inquisition/phantoms, telepatic contact.
My take is that it would look like creating a character for VtM/WtA with their blood disciplines/auspices (?)
I like it