Vendra, Vastwood Vine Maiden

{g} in your mana pool doesn't empty until your opponent's end step.
Landfall—Whenever a land enters the battlefield under your control, create a 1/1 green plant creature token with "{t}: Add {g} to your mana pool." If you control three or more plant creatures, instead create a legendary 1/1 green avatar creature token with "This creature gets +1+1 for each {g} in your mana pool."