Hardened Scales decks have a new fancy toy to play with.
Hardened Scales' power level can be massive. If you consider the effect of Solidarity of Heroes, which doubles the number of +1/+1 counters on Stonecoil Serpent for mere two mana, you have a powerful card in your hands.
That would be more than enough to swing for lethal damage early on in a match-up. It also dodges a large number of multicolored removals, such as Terminate, Assassin's Trophy, and Abrupt Decay.