It turned out that Xyler's training was more confusing than it was useful.
Zero wasn't allowed to use his Darkness Manipulation System at all and he had to take off his Shade's Helm for the duration of training. He could only use his Combat Archery System - Xyler, with his unknown magic, had set up a range of moving targets. Several blue spheres that could move in literally any direction and if he managed to hit one of them with an arrow, the color would change and that specific sphere would move faster as well as slightly more sporadic than the others.
He wasn't allowed to stop until all of the spheres had been shattered, even if his energy was almost gone.
Zero had hit at least 4 of them by this point and they were a lighter shade of blue than the remaining 2. While those 2 were moving in a uniform line off to one side, the other 4 had split up in different diagonal-like movements.