From the Super Mario Wiki
A Witch is an enemy in Wario World, appearing in Mirror Mansion.
Witches are magical beings that wear purple robes and half-white, half-purple masks. They attack Wario by firing bolts of electricity at him. Witches, however, are invisible. They can only be seen in the reflection of the many mirrors around the Mansion. Wario must use the mirror to determine the position of the Witch. Witches may also appear and disappear at will.
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