Is there a window for reactions after resolving each effect of the chain, or can you only add to the top of the chain and wait for all of it to resolve?

Ruling: There is a window to react after each item on the chain resolves. After each resolution, the player who controls the most recent item on the chain becomes the active player, and all relevant players must pass again to proceed.

Sequence:

• Reaction level abilities and triggers are added to the chain one by one
• Effects resolve in stack order after both players pass in succession
• After each item resolves, a new window opens where players can add more items to the chain
• All relevant players must pass again before the next item resolves