Answering the toughest questions in Magic is about walking fine lines. It's about striking perfect balances. Power and consistency, risk and reward, speed and staying power.
Flexibility is an important concept when it comes to finding balance in Magic. Choosing flexible cards or building flexibility into the structure of your deck will lower your risk and increase your consistency. In other words, flexibility helps prevent things from going wrong. If flexibility doesn't come at the cost of too much power, you should jump at the opportunity!
A modal spell is simply a spell that asks you to choose "modes" when you cast it. Abzan Charm is an excellent card because it offers three distinct options, tailored to fit your needs under varying circumstances.
Modal spells are, by nature, very flexible cards. In the middle of a hairy combat step? Add two +1/+1 counters! Troublesome creature on the other side of the board? Exile it! None of the above? Cash it in for two new cards!
If you were to separate Abzan Charm's modes into three separate cards, it's possible that none of them would be good enough for competitive play in Standard. However, combining all of the options into one neat package makes it one of the best cards in the format. It greatly increases the likelihood that the Abzan player will have the right tool in any situation. In my opinion, the flexibility of Abzan Charm is one of the things that's made Abzan the most successful deck in Standard!
Recall that mana sinks are cards that, while not necessarily expensive in themselves, can make use of your extra mana in late-game scenarios. They increase the consistency of a deck by providing insurance against mana flood.
Mana sinks are flexible cards. If they aren't expensive to put into play, they won't make your deck slow, top-heavy, or reliant on having tons of mana. However, they're also helpful if you do draw too many lands, or if the game is dragging on into the very late stages.
Cards with "X" in the Mana Cost
One particular category of mana sink is cards with "X" in their mana cost, like Hangarback Walker. "X" means flexibility! It means that you can spend however much mana you please, and the card's effect will scale accordingly.
Hangarback Walker is an extremely good, flexible card. You can put it into play right on turn two, but if you draw it on turn eight, you can make it much bigger.
Today's preview card from Battle for Zendikar follows in the same vein as Hangarback Walker.
Endless One is also a creature with "X" in its mana cost. You can cast it early if you need to do so in order to keep pace in tempo. Later in the game, though, it can easily be the biggest creature on the table!
One of the greatest appeals of a card like Endless One is its ability to plug a hole in your mana curve.
Imagine that your goal is simply to use all of your mana to cast creatures on every turn. Ideally, you'd want to cast a one-mana creature on turn one, a two-mana creature on turn two, a three-mana creature on turn three, and so on. To maximize your chances, you can build your deck with a healthy mix of creatures at each of these mana costs. Inevitably, though, you're going to have games where your draws don't line up the way you were hoping. Maybe you have a one-drop and a two-drop, but you're missing a three-drop. Maybe you miss your land drop on turn five and can't continue moving up the mana curve.
Endless One guarantees that these things won't happen. On any turn, with any amount of mana, you can spend it on Endless One!
That's the real beauty of flexibility—it helps you in the games where your draw isn't perfect. It raises the floor for how bad things can go for you and ensures that you have something to work with in each and every game you play.
Flexibility is an important factor in striking the balance between power and consistency. Playing with flexible cards will always increase your consistency, but will sometimes come at the cost of power.
Endless One | Art by Jason Felix
You can cast Hangarback Walker for two mana, but you'd usually prefer to cast Fleecemane Lion instead. You can cast it for four mana, but you'd prefer a Siege Rhino. You can use Abzan Charm to take care of Polukranos, World Eater, but Ultimate Price can basically do the same job for one less mana.
Your flexible cards will rarely let you down, but they'll also rarely be the best possible play you can make on a given turn.
Thankfully, Endless One doesn't force you to give up too much power for the sake of flexibility. Yes, spending four mana for a 4/4 isn't quite a Siege Rhino, but it's still a good rate and is likely to be one of the biggest creatures on the board.
Endless One also has the advantage of being colorless, making it playable in any deck, immune to Ultimate Price, and positioned to play well with any colorless-themed cards that appear in Battle for Zendikar. However, it's not an artifact for the purposes of being destroyed by Kolaghan's Command or Conclave Naturalists.
It's a good habit to always keep an eye out for flexible cards. You'll find flexibility in Endless One. More importantly, though, you'll find it in any quality card that strikes a healthy balance between power and consistency. Putting cards like Endless One into your decks will lower the chances of a bad draw, but they won't cost you much in terms of raw power. It's a slam dunk!