The perfect character for Fontaine 

That would be a "wolf in sheep's clothing" (something bad pretending to be something good). That said, what you just said literally feels like: she makes a façade of being a crazy selfish person, but is actually someone who is pretending to be convinced to join you only to then backstab you as the awful selfish person she had already portrayed herself to be? Haha. Reminded me of ATLA and Sokka's plan to "invite Zuko under the pretense he'll be their prisoner as he had previously offered, only to jump at him and really make him their prisoner, so he'd never see that coming." XD

@@123leyang321 No, I am trying to say Arlecchino is a good person pretending to be bad which is why I said 'sheep in wolf's clothing'. She's pretending to be someone who will betray the Fatui only to actually be their most loyal agent.