Mirrored Reflection

Playing the entity is the cost of the spell, so you need a Water entity costing 5 or less in hand to cast it. That entity is played, so its On Play happens. With 3 IKZ you can have a 5-cost like Drowncalling Siren in the Garden on your third turn.

You pay for it next turn. Two of your tapped IKZ stay tapped through your next Reset phase, so that turn starts with 2 IKZ fewer. Hydromancy Gate and other untap effects can’t refresh them before that Reset either, only after it. Over the two turns you have spent 5 IKZ for a 5-cost entity: the gain is having it a turn early.

Your opponent may also play an entity costing 5 or less into their Alley; our read, as with Drowncalling Siren, is a free play from their hand. It still has to come through their Gate, one per turn with cooldown, so it costs them tempo to use. The gift is smallest when their hand is nearly empty and largest when they hold a strong 5-cost.

Their fuller Alley helps Gathering Tide, Rowan, which costs 1 less once they have 2 or more entities there. It turns off Sentinel of Passage, Usui, which needs their Alley empty.

It can’t play Submerging Tides, Inoe, which costs 6.