If Skysplitter is the 2nd card played in a turn and Darius Trifarian is the only unit on board, how much does Skysplitter cost?

Ruling: Skysplitter costs 3. The cost is determined before the card resolves or is played.

Nuances:

• Cost determination happens before resolution, so Darius's effect (which triggers when you play your second card) doesn't affect Skysplitter's cost since Skysplitter itself is that second card