Mafiascum.net

2 Mafia Framer
1 Town Cop
1 Town Backup Cop
5 Vanilla Townies

Framing causes a player to appear guilty to a Cop, even if they are town. Framing is a factional action, so scum can only frame one player every Night even with both alive, but can always be used along with the night kill.

Does this seem balanced? And fun?

I would suspect balanced yet not fun. The play of refusing to lynch a claimed or breadcrumbed guilty result just because it might have been a frame job is too low EV for the town to ever accept, no matter how dayplay is going. So the mechanic plays out identically to cop, but fails X% of the time.

So it's more balanced than Cop but no funner than cop.
A possible improvement that I think would make it a lot more fun without changing the theoretical win %s much at all would be to let the mafia submit a frame target per perspective per townie. "If BulletNLynchProof is the cop, frame popsofctown, but if popsofctown is the cop, frame implosion". The frames get a lot more accurate, which can be counteracted by a cop who intentionally investigates someone he isn't tunneling, and that metagame seems cute and interesting. And maybe in some cases that'd be enough to make the decision to lynch the results less automatic.

I think this might play out as scumsided (allowing for 2v7 + one cop being roughly balanced). Guilties more or less can't be trusted, and 3/X slots at a time will return a guilty. I think the ev of cops usually comes from innoing or guiltying reasonably predictable slots (avoiding obvious lynches or transparently towny players), which scum can just target for the frame.

The backup cop and cop are confirmable slots themselves which is somewhat helpful for town ev but probably not more meaningful than just having a standard cop.

I am probably a little unfun but when I ask myself whether I'd play it the answer is kinda just "why not just play cop 9er?"