Mordullu's Promise is a legendary axe in Diablo III, added in patch 2.4.0. It requires character level 70 to drop. The unique affix restores Mana instantly upon cast, effectively making Firebomb a way to quickly recover from even the most costly spells. However, for the purpose of Depth Diggers and Boyarsky's Chip, it will still not make Firebomb a Primary skill.