Mistake

An enemy found in the Soul Sanctum.

Tactics
They aimlessly move back and forth, charging at the Hollow Knight when they notice him. Ending their misery is quite simple, so they mostly serve as a way to gather additional SOUL and heal up after the brutal battles against Soul Twisters.

However, they may occasionally appear out of thin air. That and the fact that they speed up upon noticing the Knight may allow them to get the occasional hit due to the surprise factor.