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...
Because then, all I need to do is be a 
soldier who doesn't have to think for himself.
لأنّني حينئذ كلّ ما أحتاجه هو أن أكون
جنديّاً ليس عليه التّفكير لنفسِه
Weil ich dann nur
ein Soldat sein muss,
porque me vuelve un soldado
que no debe pensar por sí mismo.
porque me vuelve un soldado
que no debe pensar por sí mismo.
J’ai juste à être un bon petit soldat,
sans réfléchir davantage.
In quei momenti, devo solo essere un soldato
che non ha bisogno di pensare per sé stesso.
Porque, assim, eu só preciso ser
um soldado que não pensa em si mesmo.
Ведь от меня требуют стать солдатом 
и не думать своей головой.