X marks the spot with today's preview card, or at least marks exactly how loyal your new planeswalker will be. It's a first because, despite the multitude of planeswalkers that we've seen, this is the first with an X in its cost. That's exciting because a planeswalker you can cast for three mana or ten mana opens up a whole new dimension of gameplay and radically changes how she fits into your deck's mana curve. As it turns out, the "she" in this case happens to be Nissa, so let's take a look at Nissa, Steward of Elements.
There's so much more going on here than on a normal planeswalker, all thanks to that little X in the upper right. Before we examine the impact of her cost, let's see what Nissa's abilities do.
+2: Scry 2.
This ability lets you ramp Nissa's loyalty extremely quickly and gives you a real benefit as a result. Scry 2 is not quite as good as drawing a card in the early game, but once lands are just blanks, it can even be better, and it increases your deck's consistency drastically either way. This is a powerful ability, and even more so, it gets her out of danger reasonably well.
0: Look at the top card of your library. If it's a land card or a creature card with converted mana cost less than or equal to the number of loyalty counters on Nissa, Steward of Elements, you may put that card onto the battlefield.
Now this is a swingy ability. Note that if the card isn't a creature or land or its cost is too high, it just stays there. Missing is a big hit, so if you want to fully utilize Nissa, you want to have a very high creature count, preferably made up of creatures that aren't too expensive. The upside is very real—putting an extra land into play or getting a three- or four-drop for free is a huge gain. This ability really rewards you for having a high loyalty count and even combos well with the first ability. Scrying a land/creature second from the top, drawing, then knowing you are going to hit is a sizable upside. Expect to see more "both on top" from Nissa players as a result and be afraid of what that means.
-6: Untap up to two target lands you control. They become 5/5 Elemental creatures with flying and haste until end of turn. They're still lands.
Because Nissa can ultimate immediately with enough mana, I didn't expect a game-winning ultimate in the lines of Ajani Vengeant or Nicol Bolas. Still, this is a very powerful ability. For eight mana, Nissa can hit for 10 immediately, and any deck with Nissa can threaten to end the game this way. The flying part is Nissa's blue aspect shining through, and it makes this much more threatening than it would be otherwise. She also kills other planeswalkers easily and overall becomes a much more aggressive card thanks to this ability, since this doesn't defend her like Elementals that other incarnations of Nissa have.
So, let's circle back to Nissa's cost. She comes down for X (plus a green and a blue), which makes her play very differently than any other planeswalker. In the early game, playing her for three mana and immediately +2-ing is going to be a very common play. That sets up using her 0 on the next turn, especially if you kept both on top, and gives her the path to ramp up to ultimate very quickly. Later in the game, playing her for five or six mana means that you can 0 right away and try to hit, especially if you need a defender. Once you hit the late game, you may want to save her for eight-plus mana, which gives you the ability to ultimate on the spot. That's a lot of different gameplay for one card, and it's all thanks to her cost.
I look forward to seeing where Nissa ends up, with the biggest restriction by far being the high creature count she demands. In the land of good mana fixing, her mana cost isn't very difficult, so it's mostly how likely the 0 is to hit. That leaves a lot of options, and Nissa has the power to be worth building around.