Can I play a reaction at the last opportunity before my opponent's turn ends, preventing them from taking further actions?

Ruling: No, there is no "end of turn" opportunity to play reactions that prevents your opponent from taking further actions. Reactions can only be played when a chain is already open (during closed states), which means if you play a reaction on your opponent's turn, they can still go back to taking normal actions afterward.

Sequence:

• A reaction requires a chain to be open (closed state) to be played
• If your opponent does nothing on their turn, no chain opens, so you cannot play a reaction
• If a chain does open (from a trigger or ability) and you play a reaction, it's still their turn and they can continue taking discretionary actions after the chain resolves

Nuances:

• End of time procedure exists and some abilities may trigger there (like Dazzling Aurora or Annie Legend), but you can only play reactions if those triggered abilities start a chain
• Once end of time procedure starts, you cannot go back to main timing
• The opponent controls when chains open during their turn, effectively controlling when you can play reactions