As Outpost Siege enters the battlefield, choose Khans or Dragons.
Khans At the beginning of your upkeep, exile the top card of your library. Until end of turn, you may play that card.
Dragons Whenever a creature you control leaves the battlefield, Outpost Siege deals 1 damage to any target. "Only the weak imprison themselves behind walls. We live free under the wind, and our freedom makes us strong." Zurgo, khan of the Mardu