Assemble the Gatewatch

Look at the top 6 cards of your library, you
may reveal up to 2 planeswalker cards with converted mana cost 4 or less from among
them and put them on the battlefield under your control. Put the rest at the bottom
of your library in a random order.
If a planeswalker entered the battlefield this
way this turn, at the beginning of the next endstep, sacrifice a planeswalker.