Can someone explain to me how the triggered ability of Psychic Corrosion would interact with Day's Undoing?

From what I understand of the stack, the triggered abilities go on the stack after each card draw due to Day's Undoing is triggered, so opponents discard two cards at each draw immediately before further effects of Day's Undoing happen, then the Day's Undoing "exile all effects on the stack" comes into play afterwards. However, I admit that it could be interpreted in a different way. Do I grossly misunderstand?

2 Answers 2


Day's Undoing will prevent Psychic Corrosion from doing anything. (Your opponents will not have to mill 14 cards.)

Although Day's Undoing has multiple effects, the card represents a single Spell when played111.1, and all of its effects must be resolved before anything else on the Stack is evaluated608.2c. Psychic Corrosion's ability will be triggered 7 times, but the abilities would not go onto the stack until after Day's Undoing has finished resolving603.3. However, because Day's Undoing ends the turn immediately upon resolution, those triggers never make it onto the stack.

Gatherer has a ruling for Day's Undoing that clarifies this explicitly:

If any abilities trigger while players are shuffling cards into their library or drawing seven cards, those abilities cease to exist when the turn ends. They won’t be put on the stack.

  • The Psychic Corrosion triggered abilities will not go on the stack, because the process of putting them on the stack only happens after the spell finishes resolving.
    – murgatroid99
    Oct 3, 2018 at 18:36
  • @murgatroid99 You're correct, of course. :) I've edited to correct my wording.
    – BJ Myers
    Oct 3, 2018 at 19:44
  • 2
    It might be worth editing to avoid saying "discard" (or really, to avoid implying that the opponents would have to discard if not for the ending of the turn) because Psychic Corrosion never makes anyone discard any cards, it only mills.
    – David Z
    Oct 4, 2018 at 0:47

Assuming you cast the spell on your turn, the triggers would go on the stack, then get exiled as the spell resolves because of how the stack works. Here's a rundown:

  1. You cast Day's Undoing and it resolves.
  2. Each player shuffles and draws, creating 7 delayed Psychic Corrosion triggers. These triggers are delayed because Day's Undoing is still resolving.
  3. The turn ends, exiling all the triggers on the stack.

Now, if you cast the spell on your opponent's turn somehow, the delayed triggers will go off after the spell resolves.

  • 3
    "Delayed trigger" has a specific rules meaning that does not match how you are using the term. The abilities are just triggering.
    – murgatroid99
    Oct 3, 2018 at 18:35
  • CR 603.7: An effect may create a delayed triggered ability that can do something at a later time. A delayed triggered ability will contain “when,” “whenever,” or “at,” although that word won’t usually begin the ability. Psychic Corrosion: Whenever you draw a card, each opponent puts the top two cards of their library into their graveyard. Creating the triggers happens when the action happens, but not resolving them until later is the chapter and verse definition of a delayed trigger. Arguing the semantics of 603.7 vs "a trigger that happens later" is needlessly obfuscating the issue. Oct 3, 2018 at 18:51
  • 1
    This is not an effect creating a triggered ability. It is just a triggered ability that exists on a permanent.
    – murgatroid99
    Oct 3, 2018 at 18:53
  • 2
    The ability in question is not being created by anything. It is simply a characteristic of a permanent. All triggered abilities have "when", "whenever", or "at", and all triggered abilities resolve after they trigger, with a priority cycle in between. That does not make them all delayed triggers. Delayed triggers are specifically ephemeral abilities that trigger after the effect that creates them. Arcbond is a good example of an effect creating a delayed triggered ability.
    – murgatroid99
    Oct 3, 2018 at 19:33
  • 1
    Day's Undoing only ends the turn if it's your turn.
    – murgatroid99
    Oct 3, 2018 at 22:33

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