When Anton arrived at Cabin, Draco and Crabbe were practicing dueling in a corner of the valley.
They traded spell for spell, and their skills were gradually coming along.
Crabbe was the only one among Cabin's little group whose soul had been twisted by Dark Magic, leaving him completely unable to cast the Patronus Charm.
That didn't mean he would fall behind the others, though.
He might have found it genuinely difficult to learn the Bone Shield Charm, which Anton had developed based on the underlying logic of the Patronus Charm, but he was earnestly studying Anton's theory of "Wizards as Gods" and making extremely rapid progress in Dark Magic.
After all, he was talented enough to cast the Fiendfyre Curse before graduation and use it to destroy Voldemort's Horcrux.
Crabbe had also once drunk diluted Fiendfyre Liquid and nearly died on the spot. (Chapter 173)
Afterward, Anton discovered that Crabbe's soul carried the scent of Fiendfyre.
The potion had been invented by Old Wizard Fiennes. Based on the theory of Potion-and-Charm Integration, it used a wizard's own Magical Power to induce magic after being drunk. It was essentially like casting the Fiendfyre Curse inside oneself, and the design was incredibly clever.
Anton had once gotten a bottle from Pedro and fed it to Old Wizard Fiennes. The effect was fantastic—absolutely brilliant. (Chapter 17)
From the perspective of Gray Magic, this "Boy Who Lived" had now gained a Magical Bloodline with an "affinity for the Fiendfyre Curse" through a twist of fate.
In fact, Anton wasn't the only one with a keen eye.
As loyal followers of the Dark Lord, the Crabbe family had been fortunate enough to receive personal instruction from Voldemort. The subject of that instruction was the Fiendfyre Curse.
During that earlier period when Draco and the