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 created this snake from the brick where 
Purple Smoke's capsule was broken.
أنشأتُ هذه الأفعى من القرميدة في المكان
الذي تحطّمَتْ فيه كبسولة باربل سموك
Ich habe die Schlange aus dem Stein erschaffen,
an der Purple Smokes Kapsel zerbrochen war.
La creé a partir de un ladrillo en el
que Purple Smoke rompió una cápsula.
La creé a partir de un ladrillo en el
que Purple Smoke rompió una cápsula.
Ho creato questo serpente dal mattone
dove si era rotta una delle capsule di Purple Smoke.
Gerei esta cobra de um tijolo
onde a cápsula do Purple Smoke rachou.