Mystic Sanctuary
Land — Island
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This land enters tapped unless you control three or more other Islands.
When this land enters untapped, you may put target instant or sorcery card from your graveyard on top of your library.
Illustrated by
Throne of Eldraine#247CommonEnglishLegality
Rulings
Oct 4, 2019
As these lands are entering the battlefield, they check for lands that are already on the battlefield. They won't see lands that are entering the battlefield at the same time (due to Scapeshift, for example).
Oct 4, 2019
If another effect puts these lands onto the battlefield tapped, they enter tapped, even if you control enough lands with the appropriate basic land type.