Waker of the Wilds

Oracle Text

XGG: Put X +1/+1 counters on target land you control. That land becomes a 0/0 Elemental creature with haste. It's still a land.

Card Rulings

9/29/2017 The land-animation effect lasts indefinitely. It doesn’t wear off during the cleanup step or when you lose control of Waker of the Wilds.
9/29/2017 If the ability targets a land that’s already a creature, that land creature’s base power and toughness will become 0/0, overwriting its previous base power and toughness. Other effects that modify its power and/or toughness (including any +1/+1 counters that were on it) will continue to apply.