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...
save Fugo and me, rather than 
taking the key back safely!
كي ينقذني أنا وفوغو، عِوضاً عن إعادة
المفتاح بأمان
um Fugo und mich zu retten, anstatt sich
und den Schlüssel in Sicherheit zu bringen!
au lieu de rentrer directement
avec la clé ?
per salvare me e Fugo, invece di riportare
indietro la chiave in sicurezza!
ele resolveu se arriscar para
salvar o Fugo e todos nós!
ты рискуешь собой, 
чтобы спасти меня и Фуго!