I've played against a deck sort of like this on MTGO a number of times, and its super good against creature decks. If I'm running B/W tokens, I get stomped every time. The creature supression is real.
However, when I run my Mardu control deck (lots of removal, Nahiri and
Elspeth, Sun's Champion) wither Withers (bad pun). All the
Scar and other removal become
dead and the creatures can't gain any traction.
There are some cards I really
fear seeing though. I've seen versions that run
Geralf's Messenger (since giving him a -1/-1 counter just removes his +1/+1 and he can undying again), and I hate trying to fight that card. It forces me to use either
Path to Exile or multiple removal spells.
I've also had people board in
Dash Hopes against me. That's crazy effective at stepping up tempo while letting cards like
Scar get boarded out.
Discard effects like
Duress and
Despise are butal.
Dreadbore is also a great sideboard option (especially now with all the plainswalkers floating around)
Really, the trick to playing wither seems to be assume you're against creatures game 1. You'll either stomp face or get shut down by control. Then pretty much the whole sideboard can be anti control cards (
Geralf's Messenger,
Dash Hopes,
Duress,
Despise,
Dreadbore), bring them all in if needed.
So overall the deck is great, and just needs a sideboard to face control matchups.