What is the proper sequence when Raven Bloom Student is targeted and the player responds with Stupefy? Does Raven start a chain or is it instantly boosted?

Ruling: Raven Bloom Student does start a chain (or adds to the existing chain). It is a regular trigger identifiable by the "when" keyword, not an instant boost.

Sequence:

• Opponent uses Void Seeker on Raven Bloom Student
• Player responds with Stupefy on opponent's unit
• Raven Bloom Student's trigger goes on the chain
• Chain resolves in reverse order