Nissa, Vastwood Seer

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.

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.

A Magic Origins planeswalker that enters the battlefield because of the ability of its front face will enter with loyalty counters as normal.