He, a level 1 receives an ability from a god to reverse anything. + becomes -, Life magic to death magic, etc. He encounters a level 500 mimic that only skins his arm a bit in a surprise attack, yes it only injured him and not gobbled him up instantly. took a good chunk of his total hp but he survived somehow and used his healing many times to restore himself to full hp.
Now, it took many casts for him to be fully restored, a level 1 healer doesn't have that much hp to begin with.
He reverses this skill so instead of healing, its damaging, life to death reversal. He one shots the level 500 mimic and the experience maxes out a lot of his skills...