Alternatively, using a narrative currency could work. “I spend this token the move this damage to me” sort of effect which then gives the GM a token to use as they please.

Good if you don’t mind more of a game-y feel, but can be a parasitic system that’s separate from the whole.

In the event that you haven't already considered this: What if it was a base reaction that everyone can do by making a check (eg. basic agility/reflex?), but a player can choose to specialize into using that action by taking a feat that would allow them to remove the check?

This is not so different from MTG/LoR assigning blockers. And it could be done checkless, forgoing the need to evaluate a dice roll saves a lot of time.

But it's still not as *fast* as the uninterrupted Hearthstone style.

On one hand, the desire to take a bullet for another character seems like a natural thing to crop up in TTRPGs. On the other, having attacks be retargeted often can slow down the game.

IDK
I'm looking for more if anyone got any

For bosses, +HP is p okay to me. If it's a well-designed enemy, I wouldn't mind fighting it for a few more seconds. +HP can be annoying on fodder units, ones where I could learn a rhythm, and then the extra HP just makes them feel a bit off when moving difficulties.

Game is Decktamer
store.steampowered.com/app/2870340/...

I gotta go back and take the other bosses on highest diffy and see all the creatures.

(Slay the Spire Lee's Waffle)