Risotto figures out that Doppio must be a Stand user that the boss trusts in deeply because he’s able to hear the noise from a certain Stand. Risotto then uses his Stand Metallic against him. Metallic is able to control magnetic force and attacks Doppio. Doppio uses the part of the boss’s power he received from him. While they’re fighting, Risotto realizes that Doppio’s personality and actions seem to be changing and he realizes exactly who Doppio is.
The way you make yourself disappear 
is by covering yourself in iron powder
وطريقتُك في إخفاءِ نفسك هي تغطية
نفسك بمسحوق الحديد
Du verbirgst dich, indem du
dich mit Eisenpulver umgibst
Y desapareces
cubriéndote con polvo de hierro
Y desapareces
cubriéndote con polvo de hierro
Tu agglutines de la poudre de fer
sur ton corps pour le camoufler
E per sparire non fai altro
che coprirti di polvere di ferro
E, para desaparecer, você
se cobre de pó de ferro
А чтобы скрыть себя, лепил 
к себе намагниченные частицы,