If I play Stupefy during my turn, can my opponent respond before Ravenbloom Student's trigger effect activates, or can I chain Ravenbloom to Stupefy to play around Defy?

Ruling: Ravenbloom Student only triggers when your spell is "played" (fully resolved). You cannot chain Ravenbloom Student to Stupefy because the spell has not been "played" yet when you're still declaring targets.

Sequence:

• Play Stupefy and declare a target
• Opponent can respond (e.g., with Defy)
• If Stupefy is countered by Defy, it was never "played" and Ravenbloom Student does not trigger
• If Stupefy resolves fully, then it has been "played" and Ravenbloom Student triggers

Nuances:

• Counter effects like Defy can target anything on the chain, not just the last thing played
• Even if something triggers when you cast Stupefy, opponents can still Defy the Stupefy itself