Neither player can declare attacks, except with Synchro Monsters. You can only use each of the following effects of "Synchro Zone" once per turn. If a non-Tuner Synchro Monster(s) is sent to your GY (except during the Damage Step): You can target 1 of those monsters; Special Summon it, and if you do, it is treated as a Tuner. During your opponent's Main Phase: You can send this face-up card to the GY; immediately after this effect resolves, Synchro Summon using monsters you control as material.
