Vigilante, Common, 1r
Attack=3N+4
Recruits -2N
N=#Brigand in enemy hand
Not bad. I suppose that in most cases it would deal 4 damage for 1 recruit or 7 damage for 3 recruits, which seems like a good baseline for a common not meeting its optimal conditions.
The potential problem is that its scaling cost doesn't apply in the very conditions when it would come into play. When the opponent is playing a deck where he has Brigands making up more than half his hand at any given time, it's probable that your recruits are going to be in the single digits as a natural result of his play. So you're left with a Common card that can deal 28 damage (not likely, but possible) at a cost of at best 1 recruit, realistically 5 or fewer (just guessing since it would be impossible to know without it being in action.) Since the opponent has no way to strategically negate the damage short of playing a full hand replacement card, what with the near-zero cost, I'd see this as overpowered.
Ideally, the additional recruit cost would be something that prevents playing the card for high damage twice in a row, but as it stands now, the opponent would have to be successfully putting recruits to 0 on every turn to manage that, and since it's common, you can expect to see it drawn a lot. I think the basic cost should be at least 4. This could be retooled to refund some recruits if there are no Brigands present so it doesn't become terrible in such a case.
And all this is ignoring the simple consideration that no Common card should be able to deal more than 20 damage by itself.
I like what you're trying to do with this. I think it just needs some adjustment.