Mountain

{t}: Add {r} to your mana pool. ({t}: Turn the card sideways. This can only be done if the card
is face-up, and otherwise can be done any time.
At the beginning of your turn, untap all cards.
Your mana pool is used to pay the casting cost of cards, shown in the top-right corner of a card. {r} mana can pay for {1} or {r}.
At the end of each step, your mana pool resets.)
(You can only play one land per turn.)