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...
It also means that Giorno 
will end up being correct!
بل يعني أيضاً أنّ كلام جورنو سيكون صحيحاً
sondern Giorno hätte auch
mit seinem Einwand recht gehabt.
¡también significará
que Giorno tenía la razón!
¡también significará
que Giorno tenía razón!
mais Giorno aura eu raison
sur toute la ligne !
ma anche che Giorno aveva ragione!
mas também que o Giorno
estava com a razão!
так ещё и Джорно
 окажется совершенно прав!