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...
Golden Wind, who's outside, 
turned that brick into a snake.
غولدن ويند الذي في الخارج حوّل
تِلك القرميدة إلى أفعى
Mein Golden Wind draußen hat
den Stein in eine Schlange gewandelt.
Golden Wind convirtió ese ladrillo
en una serpiente en el exterior.
Golden Wind convirtió ese ladrillo
en una serpiente en el exterior.
grâce à Golden Wind, dehors.
Golden Wind, da fuori, ha tramutato
quel mattone in un serpente.
Lá fora, o Golden Wind transformou
aquele tijolo numa cobra.
Мой стенд остался снаружи
и превратил этот кирпич в змею.