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...
Listen up... Like I said at the start, 
you're already done for.
اسمع... كما قلتُ في البداية، انتهى أمرُك
Hör mir gut zu. Wie ich schon
meinte, bist du erledigt.
Escucha… Tal como te dije,
estás acabado.
Escucha… Tal como te dije,
estás acabado.
T’es bouché ?
Je te l’ai dit dès le début,
Senti...
Escute bem...
Como eu disse, você já era.
Пойми, я сразу сказал:
тебе от меня не спастись.