The duel began in that unremarkable little park, but unlike the cataclysmic start the other audience members had imagined, the two black-robed wizards both cautiously began using magic to probe each other.
Voldemort, who had originally been furious enough to attack outright, looked somewhat puzzled. After his investigation, he knew perfectly well that Allen's wandless casting was likely somewhat superior to his own, but while magic not cast with a wand would not be weakened for beings like them, it would still lose the wand's amplification. Voldemort had never expected Allen to truly bring such a large staff as a practical combat tool—something like that, though it amplified more than a wand, also slowed casting as a result, and had all but been eliminated in the modern age. Only people like Lucius or Mad-Eye would hide a wand inside a cane or walking stick out of affectation or for concealment.
Allen could sense that Voldemort was probing him just as he was probing Voldemort. He then activated the prophetic ability of his Prophecy Eye, and after that, the defensive methods and tactical arrangements Voldemort might use came into Allen's mind—but Allen only treated them as reference. As a form of rapid prophecy, the information it detected was only the other party's intention at the moment the ability was cast, and Voldemort might even change his mind and adopt another tactic for offense and defense precisely because he noticed Allen's Prophecy Eye activating.
"Tom... it seems I should be bringing you a few surprises today?" Allen asked Voldemort. "Don't you think? I thought you'd be even more aggressive than last year... I didn't expect you to be quite so cautious..."
"You are testing my patience, boy. There are only two things I can guarantee completely..." The veins on Voldemort's bald head