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...
I-It looks like luck hasn't 
completely abandoned me!
!يبدو أنّ الحظّ لم يتخلَّ عنّي تماماً
F-Fortuna scheint mich noch
nicht ganz vergessen zu haben.
¡Parece que la suerte
no me ha abandonado!
¡Parece que la suerte
no me ha abandonado!
Le coup de bol !
La fortune m’a pas abandonné !
A-A quanto pare la fortuna
non mi ha ancora abbandonato!
Parece que a sorte ainda
não me abandonou!
Удача… ещё меня не покинула!