Each turn, a hero gets Mighty Deed points equal to their levels, and they're free to expend them - there's no saving them for another turn. They're closest to the hero power pools in Middle-Earth, but more generic. They also go down as your hero loses stamina points and thus levels: really no hero-hammering your way out of this one! Even the mightiest hero can be bled via a thousand cuts.
Screenshot of Midgard QRS sheet centered on the heroic deeds part
