Nissa, Vastwood Seer // Nissa, Sage Animist

The back face of a double-faced card (in the case of Magic Origins, the planeswalker face) can't be cast.

You can activate one of the planeswalker's loyalty abilities the turn it enters the battlefield. However, you may do so only during one of your main phases when the stack is empty. For example, if the planeswalker enters the battlefield during combat, there will be an opportunity for your opponent to remove it before you can activate one of its abilities.

If a land becomes a creature but hasn't continuously been under its controller's control since that player's most recent turn began, it won't be able to attack and its abilities with {T} in the cost (including mana abilities) won't be able to be activated. In other words, look at how long the permanent itself has been under your control, not how long it's been a creature.

A double-faced card enters the battlefield with its front face up by default, unless a spell or ability instructs you to put it onto the battlefield transformed, in which case it enters with its back face up.

The mana value of a double-faced card not on the battlefield is the mana value of its front face.

You can activate Nissa, Sage Animist's second ability even if you already control an Ashaya, the Awoken World. Just after the second token is created, you'll choose one to remain on the battlefield. The other will be put into your graveyard and subsequently cease to exist.

Nissa, Vastwood Seer is exiled as a result of her second triggered ability. If she enters the battlefield while you control seven or more lands, she won't automatically be exiled and transform.

Each face of a double-faced card has its own set of characteristics: name, types, subtypes, power and toughness, loyalty, abilities, and so on. While a double-faced card is on the battlefield, consider only the characteristics of the face that's currently up. The other set of characteristics is ignored. While a double-faced card isn't on the battlefield, consider only the characteristics of its front face.

In some rare cases, a spell or ability may cause one of these five cards to transform while it's a creature (front face up) on the battlefield. If this happens, the resulting planeswalker won't have any loyalty counters on it and will subsequently be put into its owner's graveyard.