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({T}: Add {W}.)
Idyllic Grange enters the battlefield tapped unless you control three or more other Plains.
When Idyllic Grange enters the battlefield untapped, put a +1/+1 counter on target creature you control.
An Island is a land with the subtype Island, not any land that could produce blue mana. For example, Mystic Sanctuary is an Island, but Castle Vantress isn’t.
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).
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.