Oath of the Ancients

At the beginning of your upkeep, reveal the top card of your library. If it's a land card, put it into your graveyard and repeat this process.
{r}, Discard a land card: Oath of the Ancients deals 2 damage to target player.
As long as you have four or more land cards in your graveyard, you may play land cards from your graveyard.