If Sky Splitter's energy cost is reduced to 0 by Anvivia, can Defy negate it since the cost is below 4, or does Defy look at the printed cost?

Ruling: Defy looks at the printed cost of the card, not the reduced cost. You cannot use Defy to negate Sky Splitter even if its cost has been reduced to 0 by Anvivia, because Sky Splitter's printed cost is 8.

Nuances:

• Cost reductions don't change the cost of a card for the purposes of effects that check cost; they just give you a discount when paying
• This same principle applies to other cost-checking effects like Kai'sa's conquer ability with Eager Apprentice
• However, Might reductions (like from Ahri) do actually change the Might value that cards see, because they modify the stat itself rather than just providing a discount