Choked Estuary
Land
As this land enters, you may reveal an Island or Swamp card from your hand. If you don't, this land enters tapped.
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Vincent Proce
Rulings
Lands don't have a subtype just because they can produce mana of the corresponding color. Choked Estuary itself is neither an Island nor a Swamp, even though it produces blue and black mana, so you can't reveal one to satisfy the ability of another.
(wotc • 2016-04-08)
If an Island or Swamp is entering the battlefield from your hand at the same time as Choked Estuary, you may reveal the other land to have Choked Estuary enter untapped.
(wotc • 2016-04-08)
If an effect instructs you to put Choked Estuary onto the battlefield tapped, it will still enter the battlefield tapped even if you reveal a land card from your hand.
(wotc • 2016-04-08)
You may reveal any land card with either or both of the appropriate subtypes. It doesn't have to be a basic land. For example, you could reveal Prairie Stream from the Battle for Zendikar set to satisfy the ability of Choked Estuary.
(wotc • 2016-04-08)
Rulings
Lands don't have a subtype just because they can produce mana of the corresponding color. Choked Estuary itself is neither an Island nor a Swamp, even though it produces blue and black mana, so you can't reveal one to satisfy the ability of another.
(wotc • 2016-04-08)
If an Island or Swamp is entering the battlefield from your hand at the same time as Choked Estuary, you may reveal the other land to have Choked Estuary enter untapped.
(wotc • 2016-04-08)
If an effect instructs you to put Choked Estuary onto the battlefield tapped, it will still enter the battlefield tapped even if you reveal a land card from your hand.
(wotc • 2016-04-08)
You may reveal any land card with either or both of the appropriate subtypes. It doesn't have to be a basic land. For example, you could reveal Prairie Stream from the Battle for Zendikar set to satisfy the ability of Choked Estuary.
(wotc • 2016-04-08)