Once Upon a Time, Manabases Lived Happily Ever After

To me, one of the most exciting Throne of Eldraine cards previewed so far is Once Upon a Time. It will improve mana bases and consistency in multiple formats. Today, I will run the numbers to provide deckbuilding insights, and I will show how it will fit in Simic Flash in the new Standard.

Once Upon a Time

How consistently will Once Upon a Time find a certain type of card?

Suppose we take a shuffled 60-card deck, remove a single Once Upon a Time, and put it on the stack. Then the hypergeometric probability to find a certain type of card in the top 5, depending on how many copies are in the deck, is given in the table below.

Hits in 60-card deck Probability of hitting with Once Upon a Time
6 42.7%
7 48.1%
8 53.1%
9 57.7%
10 61.9%
11 65.8%
12 69.4%
13 72.6%
14 75.6%
15 78.3%
16 80.8%
17 83.0%
18 85.0%
19 86.9%
20 88.5%
21 90.0%
22 91.3%
23 92.5%
24 93.5%
25 94.4%
26 95.3%
27 96.0%
28 96.6%
29 97.2%
30 97.6%
31 98.0%
32 98.4%
33 98.7%
34 98.9%
35 99.2%
36 99.3%
37 99.5%
38 99.6%
39 99.7%
40 99.8%
41 99.8%
42 99.9%
43 99.9%
44 99.9%

To put this into perspective, consider a typical Standard deck with 22 lands, 22 creatures, and 16 noncreature spells. For this deck, Once Upon a Time will hit a land 91.3% of the time and a creature 91.3% of the time. That is reliable, so you will consistently find whatever your hand is missing, thereby increasing the likelihood that you start the game with a good mix of lands and creatures. Whiffing (i.e., seeing five noncreature spells) is extremely unlikely and will happen only 0.1% of the time with this deck.

Once Upon a Time will help find your best creatures. Suppose your deck revolves around 8 key creatures (say, 4 Frilled Mystic and 4 Nightpack Ambusher). Then you will hit one 53.1% of the time. This means that if you add 4 Once Upon a Time to a Simic Flash deck, you effectively go from 8 to 10 four-drops. It does come with the slight downside that you have to reveal the creature, but the increase in consistency will be more important.

Once Upon a Time will also improve your mana base. For example, if you run 17 blue-producing lands, then Once Upon a Time will hit a blue source 83.0% of the time. For mana base purposes, in a deck with 14-20 blue sources, I would count 4 Once Upon a Time as approximately 3 blue sources. This can help cast double-blue cards like Essence Scatter on curve.

To make room for 4 Once Upon a Time, I’d usually cut 2 creatures and 2 lands

To explain my thought process for cutting 2 creatures and 2 lands, suppose you start with 24 lands, 24 creatures, and 12 noncreature spells and somehow decide to add 4 Once Upon a Time.

Then based on the numbers from the table above, you could treat each copy of Once Upon a Time as 0.913 lands and 0.913 creatures. Multiplying by four, you have now effectively raised both your land count and your creature count by 3.652 – 2 = 1.652. This is a simplified way to look at it, as it sidesteps the mana cost, but this does indicate that Once Upon a Time reduces the risk of mana screw in the early game and the risk of mana flood in the late game.

The resulting improvement for colored mana is huge

Consider a blue-green deck with 14-20 blue sources. Since Once Upon a Time is at least 75% hit a blue source, I would count 4 Once Upon a Time as approximately 3 blue sources for this deck. So if we cut 1 Forest, 1 Island, and 2 creatures for 4 Once Upon a Time, then we have effectively raised the number of blue sources by two. That’s huge! It’s the same as you would get when you replace 2 Island and 2 Forest with 4 Hinterland Harbor.

Mark Rosewater said that there is not a rare dual land cycle in Throne of Eldraine. So mana will be poor post-rotation, but Once Upon a Time can alleviate some of the colored mana issues. I love this.

Once Upon a Time is not a Leyline

Unlike Leylines, you don’t have to use Once Upon a Time right away. If you are on the draw, then you can take your first draw step before firing it off. And if don’t have a one-drop, then you can even wait until turn 2 to get more information on what your opponent is playing and on what your next draw step provides. This is particularly relevant for decks without one-drop creatures.

When playing Jund Dinosaurs, I often wanted to hold Commune with Dinosaurs on turn one, as I wanted more information from my draw steps to figure out if I needed lands or creatures. With Once Upon a Time, you can just take another draw step, see if you draw land or creature, and then cast a still-free Once Upon a Time with more information.

Along the same lines, on your first turn of the game, you can play Island, Once Upon a Time, and respond by casting Opt. Since you cast Once Upon a Time first, you were able to cast it without paying its mana cost. But since Opt resolves first, you have more information when Once Upon a Time resolves. Information matters for decision making, and these are the timing tricks that can give you a small edge.

Over your first 12 cards, Once Upon a Time will cost less than one mana on average

To analyze how much mana Once Upon a Time will cost in expectation, I will make the following assumptions:

  • We are playing a 60-card deck with a certain number of Once Upon a Time.
  • There are no mulligans.
  • The first Once Upon a Time we see in our top 8 cards is free. The top 8 represents turn one on the draw or turn two on the play. For a deck that will play a one-drop about half of the time, this is a reasonable cutoff where the first Once Upon a Time will be free.
  • Additional copies of Once Upon a Time in our top 8 cost two mana. So we pay full price for any Once Upon a Time beyond the first.
  • After the top 8, we draw 4 more cards, representing draw steps until turn five on the draw or turn six on the play. Any Once Upon a Time drawn from that set will cost two mana. This is reasonable for a deck that will almost always have a play by turn two.
  • After drawing the top 12 cards, the game either ends (which is not unreasonable on turn six) or we have ample mana (spending two mana in the late game is irrelevant).

Based on these assumptions, I got the following results:

Deck P(free copy in top 8) E[two-mana copies in top 12] E[mana cost]
4 Once Upon a Time 44.5% 0.355 0.888
3 Once Upon a Time 35.4% 0.246 0.819
2 Once Upon a Time 25.1% 0.149 0.746
1 Once Upon a Time 13.3% 0.067 0.667


  • The first column describes how many copies of Once Upon a Time are in the deck.
  • The second column represents the probability that you draw at least one in your first 8 cards.
  • The third column represents the expected number of additional copies (for which you must pay its mana cost) you draw in your first 12 cards.
  • The fourth column describes the expected average mana cost of all Once Upon a Time drawn in your first 12 cards. As an example, if your opening hand contained a single Once Upon a Time and you drew another on turn 4, then the average mana cost would have been one. The table shows that in expectation, the average mana cost is a bit lower, even if you run a playset.

Based on these numbers, I would evaluate Once Upon a Time as an instant-speed, undercosted Commune with Dinosaurs without the tribal restriction. That’s really good!

Many decks will want 3 or 4, but how many copies should you run?

Having a free Once Upon a Time in your opening hand is great. Paying two mana for a card selection spell is not. (It’s not terrible given that cards like Anticipate have seen play in Standard, but it’s not something that most decks are interested in.) How to balance this trade-off?

In an article entitled “How many copies of any given card should you put in your deck?” I argued that you should run 4 copies if you want to draw the card as early as possible and that you should run 3 copies if the card is good but you prefer not to draw multiples. For most decks interested in Once Upon a Time, both statements apply, so it’s a close call.

Ultimately, the decision between 3 or 4 copies really depends on your deck. You could look at the preceding table and ask yourself whether you are okay with an expected mana cost increase of 0.07 in exchange for a free copy probability increase of 9.1 percentage points. But evaluating this trade-off really depends on how valuable a two-mana Once Upon a Time would be for your deck, what you would cut for the fourth copy, how bad your mana base is otherwise, how many turns per game you expect to play, and a plethora of other factors that aren’t easy to evaluate without playing actual games. Some decks may want 3; others may want 4. It really depends.

Will it make mulligan decisions more difficult?

For context: Smaller effective deck sizes are great because this allows you to draw your key cards more often. Nevertheless, cards like Street Wraith and Mishra’s Bauble have seen little Modern play outside of discard/artifact synergies. A key reason is that they make mulligan decisions more difficult. If your opening hand contains one land, Street Wraith, and five great spells, then you’re not sure whether Street Wraith will decide a land or not, so you may have to mulligan more often.

Compared to these cantrips, Once Upon a Time is far more reliable and won’t complicate mulligan decisions as much. After all, looking at five cards is far better than drawing one random card. As long as your deck contains 21 lands, you can be 90%+ sure that Once Upon a Time will find a land, which is reliable enough to allow you to keep some one-landers. Still, 90% is not 100%, so there’s still a small chance that you will keep, whiff, and lose to mana screw.

The fewer lands in your deck, the more often this happens, which may be an issue for land-light decks in Modern. I may therefore prefer 3 rather than 4 Once Upon a Time for such land-light decks.

The card has a lot of Modern applications

Once Upon a Time enables any green deck that needs certain creatures to win. Amulet Titan, Devoted Vizier, Bogles, Infect, and Neobrand all come to mind. These decks could likely benefit from the addition of 3 Once Upon a Time, likely cutting a land, the worst creature, and some flex slot(s). I plan to simulate some of these decks in more detail in the future to gain further deck building insights.

Azusa, Lost but SeekingPrimeval TitanSimic Growth ChamberGriselbrandSlippery BogleDevoted DruidVizier of Remedies

Once Upon a Time can also improve the consistency at which Tron can find Urza’s Mine, Urza’s Tower, and Urza’s Power Plant on turn three. However, Tron runs few creatures, so Once Upon a Time will be a poor topdeck in the late game. For that reason, I would start with only one or two copies in Tron.

In Standard, Simic Flash is a great home

For the new Standard, there are several decks with hefty multicolor mana requirements that are based around specific creatures. For example, Naya Feather, Temur Elementals, Bant Ramp, and Simic Flash. I expect that Once Upon a Time can greatly improve the unreliable mana base of the decks.

In particular, the card will shine in Simic Flash. Reaching UUGG for Frilled Mystic by turn four is no small feat, and Once Upon a Time will help provide that more consistently. Also, the entire strategy is based around key flash creatures, which Once Upon a Time will provide more often. Finally, instant speed is huge for this deck: you can hold up mana and choose between a Quench or Once Upon a Time, and an instant-speed Once Upon a Time will even trigger Brineborn Cutthroat.

MTG Arena recently introduced the Standard 2020 event, which only allows cards from Guilds of Ravnica onward. Out of the 17 decks I tried, Simic Flash performed the best for me. My record with the deck so far is 12-0, beating multiple Teferi, Time Raveler along the way. And I haven’t even been able to include some of the new Throne of Eldraine goodies!

I expect that Simic Flash will be a big player in post-rotation Standard. Here is how I would build it, using the Throne of Eldraine cards that have been revealed so far.

Simic Flash

8 Island (335)
5 Forest (347)
4 Breeding Pool
4 Temple of Mystery
1 Thornwood Falls
4 Frilled Mystic
4 Brineborn Cutthroat
3 Spectral Sailor
4 Nightpack Ambusher
3 Wildborn Preserver
1 Hypnotic Sprite
4 Once Upon a Time
3 Essence Capture
4 Sinister Sabotage
2 Negate
3 Unsummon
1 Opt
2 Quench

Compared to my deck from the Standard 2020 event, I replaced the underperforming Faerie Duelist with the amazing Wildborn Preserver from Throne of Eldraine, and I replaced 3 Anticipate and 2 lands with a 1 Opt and 4 Once Upon a Time.

I also added a speculative Hypnotic Sprite to get the creature count up to at least 19, which corresponds to an 86.9% probability of hitting a creature with Once Upon a Time. That’s low—honestly a bit lower than I would like—but I think it’s still acceptable given that you need many noncreature spells for a flash strategy.

What I like most about Hypnotic Sprite is that Once Upon a Time can grab adventure creatures. That’s both flavorful and powerful: Once Upon a Time, you can potentially take removal or countermagic. This flexibility will be quite valuable in Standard, and I expect that many black-green decks will exploit this with Murderous Rider.

Once Upon a Time will improve mana bases, make decks more consistent, and has the makings of a multi-format staple.

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