Sam felt like the most straightforward method is brute force.
When he used the observation ability on the mirrors, he noticed the effects of his attacks.
From the image, the mirror didn't seem like it is damaged, but the structure inside the mirror is clearly damaged.
Sam just kept the observation ability activated and threw another attack, he could still see new cracks appearing inside the structure, they are small and insignificant, but the damage would definitely accumulate.
From what he knew, that might as well be the method of cracking.
But Sam observed something else.
That is the mirror is not exactly a solid thing. In fact, it is not even a proper mirror. It is some sort of illusion device. The arrow image is actually a projection of the arrow that is coming from outside, one side will be projecting the image, and the rest of the reflections.
