Mystica, having expressed so many spirit beasts, won't fall for such a cheap skill. She was battling with her ancient spirit spear. She was making use of her mirage skill on the spear.
She confused her prey with so many fake spear spins before hitting her desired spot.
When she hits her marks, there is a lapse in the movement of the spirit desert fox. It is an opportunity for Mystica. She stabs at other critical parts of the spirit desert fox two to four times.
If there was a health bar, the life health bar of the spirit desert fox would have shown it was a war of attrition, but this was different. No game mechanism here.
When Mystica strikes at a sure death organ, the spirit desert fox will instantly die.
The fight continued. Mystica trades strikes for the spirit desert fox claw. This went on till the spirit desert fox succumbed to its injury.
Mystica separated its head from its neck.