5e: Sacrificing Hit Dice as part of the cost of a spell

[Suralin]

So I'm trying to implement something Blood Mage-y, where sacrificing Hit Dice can be used as part of the cost of the spell. I'm not sure if that can make its way into the Cast button for the sake of simplicity, but even so, what would the syntax be for the effect in order to increment Used HD? In this setup, the player would mark off the spell slot, then click the Effect button to sacrifice an HD, *then* roll attack. I'm just not sure how to get the effect to trigger properly, or if there's a way to do that.

I'd also want to add a null "Sacrifice Hit Die" 'spell' in the cantrip list so the player would have that on hand for using sacrificed dice to power their normal spells. Doing all this manually by going into the Character screen would be a pain for my players and I'd rather not have that be the only option.

[superteddy57]

This sounds like it would be best as an extension and need to be coded to do the automation you are looking to accomplish.

[LordEntrails]

There is no effect taht modifies or uses hit dice. You will have to either handle it manually or write an extension.