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...
Can you even imagine what's 
going on over here?
هل يمكنك أن تتخيّل حتّى ما يجري هنا؟
Hast du eigentlich eine Vorstellung,
was hier drüben gerade geschieht?
¿Tienes alguna idea
de lo que ocurre por aquí?
¿Tienes alguna idea
de lo que ocurre por aquí?
Non immaginerai mai come sta
messa la situazione qua dietro...
Quer saber o que está acontecendo ali?