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...
You're not getting the key!
!لن تحصل على المفتاح
Du bekommst
den Schlüssel nicht!
¡No conseguirás la llave!
¡No conseguirás la llave!
Je te donnerai pas la clé.
Non ti permetterò di prendere la chiave!
Você não vai ficar com a chave!
Я не отдам тебе ключ!