Mi accepted the power of the God of Evil after its partner died and from that time on, the tribe was killed and eventually exterminated, whereas Mi's body was taken over by the power of the God of Evil. Anything that was filled with evil would attract the God of Evil to their body, causing their condition to worsen. This caused the dirty evil to cover its body in a black liquid.
[The Moonlight Lake can purify anything, but it cannot cleanse the evil in Mi. If it goes near the Moonlight Lake, it would contaminate the lake.] It was also painful for the Rhinoceros Beast to prevent its closest partner from getting close.
But as the last protector of the Forest of Freedom, he had to protect all the living beings.
Not only this vegetation, anything the evil aura around Mi affected, would experience something terrifying. Their pure souls could die because of the evil, while the evil souls could become crazier because of the God of Evil.