Ashaya, Soul of the Wild (SLD 2014)

Legendary Creature — Elemental • Mana cost: {3}{G}{G} • Secret Lair Drop • Mythic

Ashaya's power and toughness are each equal to the number of lands you control.
Nontoken creatures you control are Forest lands in addition to their other types. (They're still affected by summoning sickness.)

Illustrated by Jordan Crane.