Osahra, Oasis Guardian

Flying, Vigilance
When Osahra, Oasis Guardian enters the battlefield, secretly choose an opponent.
Lands you control have "{t}: add one of any color
of mana to your mana pool"
Reveal the chosen player: prevent all combat
damage from creatures controlled by the chosen
player.
{w}{u}{u}: target player other than chosen player
can't cast spells this turn. Use this ability only
after the chosen player has been revealed.