When Nissa, Vastwood Seer enters the battlefield, you may search your library for a basic Forest card, reveal it, put it into your hand, then shuffle your library.
Whenever a land enters the battlefield under your control, if you control seven or more lands, exile Nissa, then return her to the battlefield transformed under her owner's control.
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+1: Reveal the top card of your library. If it's a land card, put it onto the battlefield. Otherwise, put it into your hand.
-2: Put a legendary 4/4 green Elemental creature token named Ashaya, the Awoken World onto the battlefield.
-7: Untap up to six target lands. They become 6/6 Elemental creatures. They're still lands.