Bippa, I wouldn't do subnp for counter that pokemon since it's absurdly easy to wall (mamo, gastro, chansey, ferro [although thunder might hurt], tyranitar, quag, Mag, hell even swampert)
I have seen people run Focus Blast on SubNP but it seems like a worse option due to the shaky accuracy, low PP, and it makes Amoonguss more of a pain with Clear Smog and HP Ice.
I'd say pick scarf but it depends on what moves you're running.