[Fenris447]

I think I've achieved all of that. There's a tag expression that allows the user to pick which sized hit die they want to reduce, limited to those on the Hero. They can choose the amount of HP for the permanent reduction, as well.

The only part I'm stuck on is resetting the HD on a long rest. I've got it working to where the player can indicate they've used an HD, pick which one they used, and the trkLeft for that HD pool will be reduced accordingly. But when they Hero takes a long rest, the total tracker for that HD pool still carries the reduction.

So hero with 8 HD uses 3 of those HD to heal himself, and another 1 HD for this feature. They have 4 left. They take a long rest. Normally they recover half their spent HD, which would put them back to 8. But the tracker for this feat still indicates that 1 HD has been used, so the HD shows as 7/8 available.

Conversely, let's say the same Hero used 4 HD to heal itself and another 2 HD for this feature, leaving 2 remaining. If it long rests, it should get 4 back. And let's say we set up the tracker to reset on a long rest. In that case, the long rest will give the Hero 4 HD back, then reset the tracker, which eliminates the other 2 reduction, and the hero will have a full 8 HD.

The only way it could work perfectly is if, when the player adds a number to the tracker, it reduces the HD's trkLeft and then immediately resets itself. Without resetting the reduction to the HD. This is where we go back to the idea of a button, which I don't think is doable without getting into Authoring Kit territory. And since the goal is to work within the bounds of LWD's 5e product, I think we're stuck.