The person hiding in the mirror was Illuso from the Hitman Team. Fugo ends up being dragged into the mirror by Illuso's Stand, Mirrorman. Fugo then summons his own Stand, Purple Smoke. Despite Giorno wanting to find Fugo, Abbacchio decides to go look for the key, since that was their mission. However, once Abbacchio finds the key, he also gets dragged into the mirror world...
It's your arm that I dragged in here!
!إنّها ذِراعك التي أسحبها إلى هنا
Das ist dein Arm,
den ich in der Hand halte.
¡Lo que traje hasta aquí
es tu propio brazo!
¡Lo que traje hasta aquí
es tu propio brazo!
Quello che ho tirato qui dentro...
Eu trouxe o seu braço aqui pra dentro!