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Like expanded on in the Cheapest mandatory loop answers, there exist game states induced by combos where card effects trigger off each other indefinitely without any further action required by the player(s).

By CR 729.4.

If a loop contains only mandatory actions, the game is a draw. (See rules 104.4b and 104.4f.)

But usually, interaction, breaking the loop and preventing the draw is still usually possible, because all players gain priority from triggers being placed on the stack.

Are there examples of infinite combos that not just do not require any actions to maintain them but are actually unstoppable/uninterruptible (by (all) opponents or all players) once initiated, because they do not allow any interaction (at all, or one(s) that would lead to a different outcome), and thus force a draw?

Perhaps by, in some way, not using the stack and instead recurring state based checks that cannot be responded to?

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    If you allow for arbitrary board states of opponents I don't think there are any unbreakable loops, because of End the Turn effects
    – Caleth
    Apr 10 at 12:32
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    @Caleth I can shut down most of that by giving both players Teferi, Time Raveler. Apr 10 at 12:37
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    @PhilipKendall is there a Time Raveler equivalent for activating (non-mana) abilities?
    – Caleth
    Apr 10 at 12:42
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    City of Solitude covers a few more cases than Myrel. I hope there's not a Time Raveler equivalent for abilities because Teferi already makes for really uninteresting play patterns. Apr 10 at 12:51
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    I know of two truly unstoppable mandatory loops that don't need any extra pieces to be unstoppable: the Lich's Mirror loop and the Enduring Scalelord loop. Of those, I think the Enduring Scalelord loop is probably cheaper to assemble and trigger: I found a way to do it for 8 mana. I disagree that the other question addresses this. Neither answer there addresses making the loop impossible to stop.
    – murgatroid99
    Apr 10 at 15:19

2 Answers 2

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I know of two mandatory loops that allow no interaction once the loop starts, one using Scalelord Reckoner and another using Lich's Mirror.

Scalelord Reckoner (8+ mana)

Scalelord Reckoner has the ability

Whenever a Dragon you control becomes the target of a spell or ability an opponent controls, destroy target nonland permanent that player controls.

The loop it creates is described in one of the official rulings on the card:

If the only nonland permanents on the battlefield are Scalelord Reckoners and Dragons controlled by players who control Scalelord Reckoners, any spell or ability that targets one of those Dragons will cause an infinite loop of triggered abilities and the game will immediately end in a draw.

This is a loop of putting triggered abilities on the stack, which triggers other abilities. No player gains priority during this process, so there is no way to stop it.

This can be set up by one player if there are not already any non-Dragon nonland permanents on the battlefield for 8 mana as follows:

  • Play Forbidden Orchard and activate its ability to give an opponent a Spirit token.
  • Play Scalelord Reckoner for 5 mana.
  • Play Cytoshape for 3 mana choosing Scalelord Reckoner and targeting the Spirit token, to make the token a copy of Scalelord Reckoner.
  • Play any 0-mana effect that targets a creature, such as Smoldering Spires.

If there are other nonland non-Dragon permanents, some amount of additional mana could be required to set up the loop. The amount will vary depending on what permanents there are.

Lich's Mirror (9-12 mana)

Lich's Mirror has the ability

If you would lose the game, instead shuffle your hand, your graveyard, and all permanents you own into your library, then draw seven cards and your life total becomes 20.

The loop it creates is described in two of the official rulings on the card (I refomatted the first one for this site):

As part of Lich's Mirror's effect, it typically shuffles itself into your library. If it does, that means that if you'd lose the game again immediately after its effect is finished, it can't help you a second time. This can occur in a few different ways. For example:

  • You have ten or more poison counters. Lich's Mirror doesn't remove poison counters. If you'd lose the game this way, you'll do what Lich's Mirror says, then you'll lose the game the next time state-based actions are checked.
  • Your life total is 0 or less and an effect says that you can't gain life. Since your life total can't be raised, it stays at whatever it is rather than becoming 20, and you'll lose the game the next time state-based actions are checked.
  • The number of nontoken permanents you own plus the number of cards in your hand, graveyard, and library is less than seven. When you try to draw seven cards as part of Lich's Mirror's effect, you'll be unable to complete at least one of those draws and you'll lose the game the next time state-based actions are checked.
  • You control but don't own a permanent such as Immortal Coil with a triggered ability that causes you to lose the game when a certain game state happens (also known as a "state trigger"), and the condition that causes the "lose the game" ability to trigger hasn't changed. If you owned the permanent, Lich's Mirror would shuffle it into your library. In this case, however, it remains on the battlefield and its ability will trigger again.

If you control but don't own Lich's Mirror, Lich's Mirror itself will still be on the battlefield after its effect is finished. If you would lose the game again for any of the reasons above, Lich's Mirror has its effect again . . . and again . . . and again. An involuntary infinite loop will be created, and the game will end in a draw. (In the case of the triggered ability example given last in the list above, it's possible that a player could cause the loop to end while the ability is on the stack. None of the loops caused by state-based actions can be stopped at all.)

As the ruling says, the loops caused by state-based actions cannot be stopped, because no player gains priority between successive evaluations of state-based actions.

The cost to set this up is 5 mana for Lich's Mirror itself, 3 mana to donate the mirror with Harmless Offering, and some amount more mana to put the opponent in the state that causes the loop. The simplest way to do that is probably by giving them 10 poison counters. This could cost 1 mana to play a Glistener Elf and then attack 10 times, or 3 mana to play the Glistener Elf, give it +4/+4 with Groundswell after playing a land, and double its power with Berserk and then attack with it once.

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Grindstone (4–6 mana)

Grindstone's ability is: {3}, {T}: Target player mills two cards. If two cards that share a color were milled this way, repeat this process.

If all the cards in the player's library share a color, and they include at least two Progenitus (If Progenitus would be put into a graveyard from anywhere, reveal Progenitus and shuffle it into its owner’s library instead.), then Grindstone's ability keeps going, forever. This all happens within a single resolving activated ability, so players do not get priority while it is happening.

With a deck that naturally meets the condition of all cards sharing a color (which can be made somewhat practical using MDFC lands), this takes 4 mana in total. Otherwise, we can use the well-known combo, adding Painter's Servant to make the cards share a color, for a total of 6 mana.

Grist, the Hunger Tide (6 mana)

Grist, the Hunger Tide also has a similar repeating-mill ability: +1: Create a 1/1 black and green Insect creature token, then mill a card. If an Insect card was milled this way, put a loyalty counter on Grist and repeat this process.

A cheap way to arrange for this to repeat forever is: Demonic Consultation, naming a card not in the deck, to exile the whole library; Pull from Eternity to get Progenitus back into the library; Artificial Evolution to change "Insect" to "Hydra" in Grist's text.

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  • Upvoted, but I think this answer would be improved by adding an explanation of what "Then repeat this process" means on an ability (specifically, that they don't use the stack). That rule is non-obvious to me and I only know it from playing Arena.
    – Tim C
    Apr 12 at 16:23
  • Your Grindstone effect would work better against a players library having two Worldspine Wurms. Apr 12 at 16:56
  • Grindstone would not create an infinite loop with Worldspine Wurm because Worldspine Wurm's ability is a triggered ability. It specifically creates an infinite loop with Progenitus because Progenitus's ability is a replacement effect.
    – murgatroid99
    Apr 12 at 17:26
  • Sphinx's Tutelage does the same thing as Grindstone but for three mana, not four, right? May 2 at 18:03
  • @PatrickStevens It's similar, but the "nonland" condition stops it from working with Painter's Servant, and the restriction to "target opponent" makes it generally less plausible.
    – m90
    May 3 at 15:19

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