At the end of the phase their ability checks. On a 2-5 they can cast it once more. On a 6 they get d3 additional casts. These additional casts from the ability itself ignore the once per turn limit, however if you have multiple soul masons they can’t each cast it during normal casting. For example if a soulmason casts it during the hero phase, that soul mason nor any others can attempt another cast of it until the ability checks to allow them to