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 need more resolve, 
but it's not too late yet!
!أحتاجُ لعزيمةٍ أكبر، لكن لم يفُت الأوانُ بعد
Das macht es schwieriger,
aber vorbei ist noch nichts.
Necesito prepararme,
pero aún estoy a tiempo.
Necesito prepararme,
pero aún estoy a tiempo.
Dovrò avere una determinazione di ferro,
ma non è ancora troppo tardi!
Vai exigir muita coragem minha,
mas ainda dá tempo!
Для того, кто смел, ещё не поздно!