Ideas I had for TP-based moves for Magni & Vesper (please ignore if you are not interested or think this is a bad suggestion!):
For Magni, his gimmick is that he has bad attack and HP, but an amazing MP stat (with a good mix of offensive and utility spells) and speed! Each turn you are only going to want him to use an MP move, because his regular attack is so weak. Maybe his TP move (costs 50TP?) could be to allow another party member to attack twice for that turn? This would be good if you do not want to use MP that turn, or if you are facing an enemy which is weak to physical attacks but strong against magical attacks (Magni is better off letting someone else attack physically than attacking himself).
Lore-wise, the move could be a speed potion, Hopium, or (if you want to name it something that implies something physical was used to make it) Magmite juice/Crushed magmites?
For Vesper, I have 2 ideas for a TP move: Revive a fallen party member or Drain enemy HP (healing Vesper). The idea is that Magni is the only person who can revive someone else (Elixir). If he dies, unless you have an item which revives you (which does not exist in this DLC), there is nothing you can do. Since Magni dies the easiest this skill could be useful to have on someone else, but it is a powerful skill so it should still be difficult to use. Maybe it could cost 100TP (or 80TP)?
Lore-wise, maybe Vesper uses a totally-not-a-vampire-move (biting a neck, setting a curse) OR he reads a dark tome/book (as a scholar) which has a healing incantation.
If this is too powerful, maybe he does an attack that drains the opponents HP and heals Vesper’s HP. Could cost 50TP? The same lore-reasons could apply here.