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...
But I was glad when he refused to 
admit defeat and left the mirror.
لكن كنتُ سعيداً عندما رفضَ الخسارة
وغادر المرآة
Aber ich war froh, dass er nicht verlieren
wollte und den Spiegel verlassen hat.
Me alegra que se negara a aceptar
la derrota y dejara el espejo.
Me alegra que se negara a aceptar
la derrota y dejara el espejo.
Mais son refus de mourir
et la fuite qui a suivi,
Però sono stato lieto che abbia rifiutato
di arrendersi e che abbia lasciato lo specchio.
Mas eu fiquei contente quando ele
decidiu fugir do espelho...
Но я… очень рад, что он 
не признал поражения и сбежал от меня.