Does Vex's Defy ability check the original printed cost or the modified cost of a card like Hextech Ray that has been reduced?

Ruling: Defy only checks the printed cost of a card, not any modified cost. Any effect that refers to a card's cost checks the printed cost.

Nuances:

• Cost reduction effects like those that reduce Hextech Ray to 2 power do not affect whether Vex can Defy it
• This principle applies to all effects that reference a card's cost