After casting a Reaction spell that draws cards, can you cast another Reaction (like a counter spell) from the newly drawn cards to respond to a spell still on the stack?

Ruling: Yes, you can cast a Reaction from newly drawn cards to respond to a spell still on the stack. Priority passes again after every link in a chain resolves.

Sequence:

• Opponent casts Catalyst of Aeons (goes on stack)
• You cast Meditation in response (goes on stack on top)
• If no one responds to Meditation, it resolves and you draw 2 cards
• Priority passes again, starting with the controller of Catalyst of Aeons
• You can then cast Defy (from the newly drawn cards) to counter the Catalyst of Aeons
• You can continue casting Reactions until you have no more answers