Mana Wraith Eric was a very unique existence.
From what Marvin knew, he was the key to opening the Secret Garden's entrance.
Back when the Wizard Apprentice named Eric was swallowed by the Magic Medicine King, a part of his soul formed into resentment.
It had a willpower that couldn't be neglected. Even though it was swallowed by the Magic Medicine King, the latter wasn't willing to digest that resentment. Otherwise it might be assimilated by the resentment.
Thus, it simply expelled the resentment from its body before pouring its own magic power in it to turn it into an independent resentful ghost with a body made of magic power.
That Mana Wraith involuntarily became the Magic Medicine King's accomplice.
After all, the real Wizard Apprentice Eric had already died and the Mana Wraith was only left with some of Eric's anger and resentment.
