The Great Deku Tree

Your unspent green mana empties only at the
beginning of your end step.
Put a -0/-1 counter on The Great Deku Tree:
Add {g} to your mana pool. Use this ability
only once each turn.
When The Great Deku Tree dies, create a 2/2
green knight creature token and a 1/1 white fairy
creature token with flying and put them onto the
battlefield. Then add {g} to your mana pool for
each -0/-1 counter on The Great Deku Tree.