From what Edgar had mentioned, Qin Ruo came to understand the Underworld's currency and exchange method.
The Undead's Mana Cores consisted of Elemental Energy, which was very useful in the Underworld. The amount of Elemental Energy would be based on the level of the Undead multiplied by ten. However, the calculation for Boss-tier monsters would be different. For instance, a Level 50 Skeleton Warrior had only five hundred Elemental Energy, but a Level 50 Miniboss had Elemental Energy of five thousand and above. Tier 5 Megabosses or Elite Bosses had even more Elemental Energy—ten thousand and above. What's more, Deathly Liches and Dark Knights had five hundred thousand and above Elemental Energy.