Eventually Cell is indeed an SK and perhaps the Mafia is constituted by the Frieza Forces or something like that.
Gambit is the fake vig
Knight is a Mafia flavour Cop which is usual
Grammaton is a Mafia roleblocker
Scenario 2 actually doesn't hold because Usopp claims to have witnessed Rej being gifted before Midnight confessed, so it would require the three of them to be part of a team probably, because Rej didn't deny. But why would a scum gift another scum if at all in the first place.
So this should be the ultimate plan:
We lynch Queen
I jail and execute Rej
Gambit shoots Usopp
Tris protects me and Midnight gifts me
Grammaton roleblocks Usopp
Although of course I can't expect all to come to fruition since scums currently left in the game are presumably 4.