This land enters tapped unless you control three or more other Plains.
When this land enters untapped, put a +1/+1 counter on target creature you control.
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.
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