Suspicioni, like his bio states, is an Oni. He has a large head, bright blue skin, and a grey horn on top of it. He has three large red eyes with blue irises, two in the front of his head, one in the back of his head. He wears a yellow loincloth with brown stripes and fluff around his neck. He's also barefooted.
Distrustful and paranoid about everything around him, Suspicioni appears to put really little faith in relationships, and he passes this attitude onto those he Inspirits.
Anyone Inspirited by Suspicioni gets filled with immense doubt and incapable of trusting even close friends. In the anime, Suspicioni achieves this by speaking directly to the Inspirited, convincing the victim that everyone else's out to get them. In severe cases, the Inspirited may experience self-doubt to the point of suffering an existential crisis.
Suspicioni appears in EP059, having Inspirited Eddie and causing him to doubt his classmates and teacher. Nate reveals Suspicioni, but before he can attempt to thwart the Yo-kai, Suspicioni switches targets to him and causes Nate to become paranoid. Suspicioni convinces Nate than none of his Yo-kai friends actually like him, and although Whisper and Jibanyan manage to get Nate to summon Blazion, Suspicioni tricks Nate into thinking that Blazion's roaring actually means that Blazion is annoyed at being treated as Nate's puppet. This causes a dejected Nate to dismiss Blazion despite the lion Yo-kai trying to tell him otherwise.
As he passes by Bear, Eddie and Katie, Suspicioni tries to convince Nate to doubt his friendships. Nate ends up summoning Tattletell so he can find out the truth for himself, and becomes relieved when his friends, under Tattletell's influence, affirm their friendship. Shocked that his suspicions have failed, Suspicioni surrenders his Yo-kai Medal. Then Whisper says that if you’re suspicious of someone, they aren’t always going to hurt you. But then he says “but they probably are...”