Magnus used multiple setups to force Alex into going all out, but after the first one, he was able to avoid them or prepare in advance to take the hit without receiving any major damage.
While Magnus was casually throwing around peak fourth and early fifth-rank spells of devastating might, Alex was facing no trouble.
Alex knew Magnus was not using his true strength because if he did, he would be in serious trouble, but even if he did, he was confident of holding his own till the time when the battle against the Quetzalcoatl reached a critical point.
Unbeknownst to Alex, while he believed Magnus's goal was to prevent his victory in the event, in reality, he was actually assessing his abilities and limitations, observing how he adapted to various battle situations.
If Alex could have heard Magnus's thoughts, to say he would be surprised would be a massive understatement.
