seitora said:
Well she has a Kyuubi as her Shikigami, but other than that, I'd say some of the extremely upper-end skills of the kitsunes would kill her (if she didn't immediately gap away).
Nah, Yukari's obscenely broken--she has nothing to worry about. Keep in mind that her control of boundaries canonically extends to the Boundaries of Truth and Lies, Life and Death, Matter and Antimatter, Dreams and Reality, Motion and Stillness, Straight and Curve, Humans and Youkai, Form and Emptiness, Wave and Particle, etc.
The most anyone in SayuMayu that we've seen so far could do is make her put forth an effort. She can literally say 'Your existence is a lie' and make you vanish from Reality, or turn half of you into antimatter and annihilate you, shift you from being alive to being dead, freeze you forever, turn you into a normal, baseline human, and a million other things.