Can I use a Defy that I just drew from Stupefy to counter a Hextech Ray that is already on the stack?

Ruling: Yes, you can use the newly drawn Defy to counter the Hextech Ray.

Sequence:

• Opponent activates Hextech Ray targeting your Stalwart Poro
• You use Stupefy targeting your Poro in response
• Stupefy resolves and you draw a Defy
• Your opponent (as controller of Hextech Ray) has priority and passes
• You receive priority and can now react to Hextech Ray with the newly drawn Defy