Can I play a reaction spell at the end of my opponent's turn before they pass priority and my turn starts?

Ruling: You cannot play spells during your opponent's turn unless they play something on the chain or there is a showdown. There is no formal "end of turn" phase where you automatically get priority.

Nuances:

• If your opponent plays a spell during their turn (like Meditation), you can respond with your own spell in reaction
• You would need to guess when your opponent is done playing cards based on their remaining mana, but cannot simply wait for them to pass the turn