Mirage wasn't that affected by the resulting spell explosion.
At most, he only suffered a bit due to the violent winds that came as a result of the explosion.
He wasn't blinded by the sudden increase in brightness as well.
Thus, he managed to see with his own eyes, how the creature had made its mad attempt to move to the side only for it to stop in place when it didn't have any direction to run to.
The strange horse creature was a really fast creature when it comes to movement speed.
However, no matter how fast the creature could move, if it couldn't even its speed to its full extent, it would still be called useless.
The place they were fighting in was a limited space, after all.
Thus, its movement was severely hindered as a result.
If they only fought outside where the area was much more spacious and complicated, then things right now would have been a lot more different.