As an exceptionally profound and dangerous form of Dark Magic, Fiendfyre's greatest trait was its ability to continually strengthen itself by devouring its surroundings.
Voldemort used this trait of Fiendfyre to completely suppress all of Quirrell's attacks.
During his years studying under Nicolas Flamel, Quirrell had devoted all his energy to alchemy, allowing him to better unleash the power of the Philosopher's Stone.
Under most circumstances, this was undoubtedly his greatest advantage.
But once that advantage was countered, Quirrell would immediately fall into an extremely passive position.
Against an ordinary dark wizard, he could still rely on the magic he had mastered to contend with them as best he could.
However, the one standing before him now was Voldemort. Perhaps disengaging from the battle and denying Fiendfyre the chance to grow was the best option.
Voldemort naturally understood this as well. The Fiendfyre serpent he had unleashed opened its burning maw and lunged straight at the distracted Quirrell the moment it finished devouring the spear.
The Fiendfyre serpent was astonishingly fast, leaving a twisted trail through the air.
Feeling the surging heat bearing down on him, Quirrell immediately beat his metal wings and rapidly retreated, beginning to evade the Fiendfyre serpent's attack.
The Fiendfyre serpent suddenly changed shape, its body instantly stretching far longer.
"Damn it!" Quirrell gritted his teeth, veins bulging on his forehead as his wings beat more frantically.
Voldemort had also changed targets. Quirrell's earlier interference had already left him seething with rage, and now he intended to press his advantage and deal with this troublesome fellow first.
Quirrell was drenched in sweat. Magical fluctuations enveloped his body, and his wings seemed to have sunk into a mire; every beat took immense effort, leaving him practically unable to move.
The Fiendfyre serpent accelerated even further, closing to