Mirror Shield (also Reflex Reversal) is a defensive shield technique: the wielder shows the shield to the enemy, who must pit its will against it, and not every will holds.
On failure the enemy is frightened and backs away, and may see itself in the shield in a terrifying way.
In the Omniporal Labyrinth a serpent saw its reflection and took fright, a cyclops saw its own red eye reflected and retreated, and a dinosaur could not resist and retreated.