If my opponent plays Hextech Ray targeting my Lecturing Yordle, and I respond with Stupefy to draw a card (drawing Retreat), can I play the Retreat I just drew before Hextech Ray resolves to save my Yordle?

Ruling: Yes, you can play the Retreat you drew from Stupefy before Hextech Ray resolves, returning the Yordle to hand and causing Hextech Ray to resolve with a null target.

Sequence:

• Opponent plays Hextech Ray targeting Lecturing Yordle
• You play Stupefy in response
• Stupefy resolves: Yordle gets -1 Might, you draw a card (Retreat)
• Priority passes back, you play Retreat
• Retreat resolves, returning Yordle to hand
• Hextech Ray resolves but the target is null and it does nothing

Nuances:

• After each action or resolution on the chain, priority passes between players
• The player who controls the top item on the chain gets priority first after a resolution
• A spell with a null target does nothing when it resolves