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...
Fugo must've been dragged into 
the mirror and disappeared,
لا بدَّ وأن فوغو قد سُحِبَ إلى داخل
،المرآة واختفى
Fugo muss in den Spiegel gezogen
worden sein, als er verschwand.
Debió arrastrar a Fugo al interior,
Debió arrastrar a Fugo al interior,
Fugo a disparu,
aspiré à l’intérieur,
Fugo dev'essere stato trascinato
nello specchio e per questo è scomparso,
Fugo desapareceu porque foi
arrastado pra dentro do espelho,
Фуго пропал, 
потому что его затянули туда,