Oh, It's from an anime called JoJo's bizzare adventure. It's basically a humanoid figure people summon to fight for them. Sometimes they have different abilities e.g: they can only be seen via a reflectionWhat is a stand?
Okay, can we go with the canon ones for a basis?
Sonichu: Red Hot Chilli Peppers. Now he can REALLY zap to the extreme!
Rosechu: NONE. Or Holly's Stand and it's killing her from the inside.
Black Sonichu: THE WORLD, Killer Queen, King Crimson, Whitesnake, Dirty Deeds Done Dirt Cheap... basically, any villain's Stand. Because he's the token badguy turned good guy and that's probably better than his current personality.
Wild: Hermit Purple, Holly's Stand, or some other plant-based Stand. Basically, something plant-related. Alternately, if we're going with his post-Simonla personality, then clearly it must be The Fool, which he'd see as Simonla's spirit.
Bubbles: Hierophant Green, since it's water-like. Or maybe something too powerful for her, like Purple Haze.
Angelica: Cream. Because she's dead on the inside.
Punchy: Star Platinum, Crazy Diamond, Gold Experience... something that punches a lot. Maybe The Hand for maximum damages.
Magi-Chan: Heaven's Door. Because Chris makes him already do all that he wants anyway.
Why is Rosechu being useful?Rosechu - Pearl Jam
Silvana should have an evil Stand too. Or maybe her Stand is her ability to change genders.