I’ve found a combination that seems rather broken to me, and I can’t find anything stating that the combination itself isn’t RAW, although it definitely seem like it isn’t RAI. However, the combination seems far too OP to be RAW, and I wanted to confirm that this is truly an acceptable use of Haste and Quivering Palm in a combination. There’s a second part to the question, assuming the first is correct.
To make this simple: a level 17 Way of the Open Hand Monk (with Quivering Palm) and a level 17 Sorcerer are in the party. The Sorcerer casts Haste on the Monk. The Monk now has 2 actions (Normal Action + Haste Action). The Monk uses his Haste Action to make one Unarmed Strike against an opponent and spends 3 Ki Points to set up the Quivering Palm vibrations in the enemy. The Monk then uses his regular action to trigger said vibrations and either drop the enemy to 0 HP if it fails the Con save, or do 10d10 damage if it succeeds.
Assuming that the Haste stays up, the Monk may do that 5 turns in a row before he runs out of Ki Points. Thinking of high-level enemies, unless they have crazy good Con saves, even with Legendary Resistances they have a decent rate of failure and this seems like an abuse.
If a 17th-level Open Hand monk has Haste cast on them, can they set up and trigger Quivering Palm in the same turn?
Assuming that the answer to that question is yes:
If that same Monk also had 2 levels in Fighter, could they not also use their bonus action and their Action Surge for an additional Quivering Palm setup and trigger in the same turn?