Indestructible (Effects that say "destroy" don't destroy that permanent. An indestructible creature can't be destroyed by damage.)
As long as your devotion to green (Each in the mana costs of permanents you control counts towards your devotion to green.) is less than five, Nylea isn't a creature.
Creature spells you cast cost less to cast.
: Reveal the top card of your library. If it's a creature card, put it into your hand. Otherwise, you may put it into your graveyard.