Attack priority of each tile
The attacking order or attack priority in which scrolls attack is determined by their position on the board. Units in the closest column to the enemy board will attack first, from the top of the screen to the bottom, followed by units in the remaining columns behind. Relative to the player, the opponents board is rotated 180 degrees. Thus, it will look like the enemy's attack priority goes from bottom to top instead. Depth works as one may expect still, from closest to furthest away from the center of the board.
Demonstration[]
The order of attack can be clearly seen in the following battle demonstration video: