Axel was exhausted.
He had spent just about a minute to a minute and a half solely focusing on controlling an entire, full-body illusion of another person. Thankfully, he decided not to attack the ghast at the same time. Lukas had yelled out not to attack it.
At that point in time, Axel reasoned he shouted it because he either saw the future or just came back from it, same thing to him. Either way, it meant Axel shouldn't attack it, which was a shame seeing as he had a perfect opportunity to...
But, instead of attacking it, he backed off and focused solely on the illusion to try and assist Lukas in whatever way he could.
