A fundamental aspect of deck building is deciding how many copies of a card to put into your deck.

Over the past few months, we've taken a look at why you would play four, three, or two copies of a card in your deck (in "Four of a Kind," "Three's Company," and "Take Two," respectively). Today, it's time to complete the cycle with the final missing entry: let's focus on one-ofs!

While playing a single copy of a card in your deck can sound pretty low-impact, that's quite far from the truth. While in an untuned deck that may be the case, in a deck deploying them properly, often a one-of makes for a crucial piece of a plan!

So, when is it right to play one copy of a card in your deck? Here are five of the main reasons you'd want to:

1. The Card Creates Inevitability

The difference between having one of a card and zero of a card in your deck is tremendous.

If your deck contains zero copy of a card, you will never draw it. If your deck contains one of a card, you are guaranteed to see it given enough time. It may take a while, but you will see it eventually.

Take, for example, Elixir of Immortality.

Let's say you want to play a deck that never runs the risk of losing due to an empty library. Playing a single Elixir curtails that possibility.

Traditionally, very slow control decks have played this card. You can draw as much as you'd like, let the game go as long as you want, and can still always recycle your cards and make sure your deck doesn't run out. You don't want more than one—but that one is a route to victory.

And it's not just this kind of slow, grinding inevitability either. There's threat inevitability also! Let's look at Entreat the Angels:

This is a card you seldom want to draw without miracling it. But playing a single copy in your deck means that, as the turns roll on, eventually you are going to find it. And no matter how stalled the board is, this will probably break that stall.

Playing one copy of a card or not can be the difference between numerous wins and losses.

2. The Card Is a Tutor Target

There's a class of cards commonly referred to in Magic as "tutors," named after cards like Demonic Tutor and Enlightened Tutor.

These kinds of cards reward diversity. When you can pick any card out of your entire deck to go get, the more options you have, the more likely it is you'll be able to find the perfect card for the situation. With tutors, it's usually better to play four one-ofs to go find than four copies of the same card.

For example, if you're playing Enlightened Tutor, rather than playing four Moats, maybe you play two Moats, one Rest in Peace, and one Circle of Protection: Red. You'll seldom need more than two Moats in a game, and if you're up against burn or a graveyard deck, you'd much rather have those other cards.

As with inevitability, the difference between having zero and one of a tutor target in your deck can decide the entire game.

Now, this can absolutely be (and often is) taken too far. (I wrote about this in "Pandora's Toolbox," which you should check out for more information.) But if you're playing with tutors, you're usually going to want to have some singleton targets.

3. The Card Is an Occasionally Unwieldly, Occasionally High-Impact Draw

Some cards are extremely powerful—but aren't cards you always want to see. They don't end up as a core part of your main strategy. They might not even always work. But they give you something to slam late game and can make a huge difference.

A good example is Loxodon Warhammer in Faeries decks.

Now, these Faeries decks ran on Bitterblossom and instant-speed plays like Mistbind Clique or Cryptic Command. So what was a three-mana sorcery-speed artifact that cost an additional three mana to get rolling doing in your deck? Well, if the game ran long, it was a powerhouse!

Faeries ate its own life total between Bitterblossom and Thoughtseize, and once it was out of gas it didn't have many ways to go up on cards. It also usually had tokens around to equip to. So while you didn't want the Warhammer in your opening hand or early, as a midgame draw it would have a huge impact.

Not every Faeries deck played the Warhammer—far from it—but some that did found plenty of success with the card. And that's just one example: you could look at it like playing an expensive card in your low-curve deck or a single big-draw spell in your aggressive deck as a way to refill on cards. Sometimes playing the "miser's one-of" can go a long way.

4. You're Splitting or Supplementing

As noted before with two- and three-ofs, when you have a bunch of very similar cards that are each better in different situations, it's often better to split them up than just play one.

For example, let's say you're building a Blue Energy Control deck and looking at threats to win the game with. Your metagame skews more aggressive, and you're trying to decide between Sphinx of the Final Word and Aethersquall Ancient as your finisher of choice.

Now, the Ancient is probably going to be better against those aggressive decks. It also fits better with what your deck is trying to do.

But against the control decks, I'd rather have the Sphinx in a long game. And since your metagame skews aggressive, a 3-1 split of Ancients to Sphinxes makes sense to consider here.

It's not just big win conditions: removal spells, board sweepers, burn—there are reasons to split them all. Instead of automatically going to four, always be asking if splitting between similarly powered cards is going to be a better route. (Plus, in playtesting, that might help you learn which one is actually better, too!)

5. The Card Is a Surprise That Can Turn the Game

For a very long time, my tournament decks of choice were white aggressive or midrange decks. And, after a while, something I started to do was main deck one Wrath of God.

Why? After all, it's a bit strange to have a curve of one-drop, two-drop, three-drop, board sweeper.

And I agree—that's not how I would recommend playing it. However, it's something that can absolutely win you the game in any kind of creature mirror. You slow your hand a little bit and let them commit tons of resources—then bam, you sweep the board out of nowhere and easily clean up the game. Few players would think to play around Wrath of God there.

Furthermore, once they have seen it and its done its initial damage, they're going to play around it in every subsequent game. They don't know there's only one in your deck—for all they know you could be packing four!—and you can have the upper hand as they play suboptimally.

Now, I'm not saying you should always play a board sweeper in your aggressive deck. Far from it. But in an aggressive metagame, it can absolutely be something to consider.

If there's something your opponent won't expect that you can craft your hand around if you draw it, that can make for a good one-of.

Four, Three, Two, One, Blastoff!

And with that all said, the compendium of how many copies to play in your deck is complete!

Hopefully you enjoyed this deep dive and journey into how many copies of each card to play in your deck and found it useful for your own deck building! May you go forth, find initial builds, and tune your deck well.

Have any questions or thoughts? I'd love to hear from you! You can always reach me by sending me a tweet, asking me a question on my Tumblr, or sending me an e-mail (in English, please) at BeyondBasicsMagic@Gmail.com.

I'll be back next week. Talk with you all again then!