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...
Damn it... My pride's not 
going to stand for that!
اللّعنة... كبريائي لن يتحمّل ذلك
Scheiße auch …
Das macht mein Stolz nicht mit!
Maldita sea…
Mi orgullo no me lo permite.
Maldita sea…
Mi orgullo no me lo permite.
Ma fierté m’interdit
de laisser passer ça !
Col cazzo... Il mio orgoglio non può
tollerare una cosa del genere!
Maldição... Sou orgulhoso
demais pra admitir isso!
Чёрта с два! 
Моя гордость этого не переживёт!