Obviously I'd rather they were obtainable through in-game means, be it "perfect" synced runs or something else.
o5n I think would be quite popular.
St mocianne's arboretum hard last boss
Final boss of puppet's bunker, yes there is something similar, but that texture is unique.
P6 or memoriate durante as a fashion accessory could be interesting since it's mostly the standard person model with extra bits stuck on for their power up.
Storm's crown curling iron form. The other form's ok, but would you really say no to the buff one?
Maybe forgiven whimsy from mt gulg?
Grand cosmos second boss
Anamnesis last boss
heroe's gauntlet all three bosses, although the second and third are more interesting than specral thief