I heard it was, but I just checked the Giants webpage and found:
Quote:Back and better than ever, Series 2 Skylanders are returning from Skylanders Spyro's Adventure with new "Wow Pow" power upgrades and increased level cap.
But Cynder's lightning-from-the-sky doesn't seem like it'll be an upgrade replacing her primary attack. So either it is replacing her primary attack, or it's a fourth move. Although even if Cynder's Wow Pow is a fourth attack, I suppose it doesn't mean somebody else's Wow Pow can't be an upgrade.
EDIT: And it can't be replacing the primary attack because it's used in the same video as the lightning breath. So that means it's a fourth move or is cast by holding the primary attack button.