NHF – new heroes for Heroes V 3.1.

The sacrifice for stats is interesting, but I would like to be able to control the amount needed for the sacrifice. However, it would be difficult to organize this nicely in the interface.

I think controlling it is a drawback; there should be a fixed amount, and it shouldn't be spammed. It should take up the entire turn, and the sacrifice should only be once a day, but it's better to leave the fine-tuning of this ability to a good game designer who can balance everything. In terms of the interface, you could use a menu similar to the demon summoning sacrifice.
P.S. By the way, it would be cool to add the effect of a wall of fire or opening a portal when using this ability.