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 was over as soon as you dragged me in.
لقد انتهى حالما سحبتَني إلى الدّاخل
Es war bereits vorbei, als du
mich hereingezogen hast.
Todo acabó cuando me arrastraste aquí.
Todo acabó cuando me arrastraste aquí.
Tu as scellé ton propre destin
en m’attirant ici.
È finito tutto nel momento stesso
in cui mi hai tirato qui dentro.
Você perdeu no momento
em que me trouxe pra cá.
С того самого момента, 
когда затащил меня к себе.