Doomsday + Thassa's Oracle

AI draft — not yet human-reviewed. Check citations and flag anything that looks wrong. How pages are reviewed.

Overview

Resolve Doomsday to set your library to the five cards you chose (search-for-a-quantity rule; [701.15d]; if your library+graveyard contained fewer than five cards, all of them become your library [Ruling [2018-03-16]]). If Thassa's Oracle then enters the battlefield and your devotion to blue (which counts in the mana costs of permanents you control, including Thassa's Oracle) is greater than or equal to the number of cards in your library, its triggered ability causes you to win the game (Thassa's Oracle oracle text; devotion counting: Ruling [2020-01-24]).

The StackRules & CitationsDetails & Edge Cases

Step 1

Cast and resolve Doomsday. You search your library and graveyard for five cards and exile the rest, then put the chosen cards on top of your library in any order; this searching-for-a-quantity is governed by [701.15d] and if library+graveyard had fewer than five cards all those cards become your library per Ruling [2018-03-16].

Step 2

After Doomsday finishes resolving, your library consists only of the chosen cards in the order you set them (subject to any replacement effects that modified the search per [701.15f]).

Step 3

Arrange the chosen five so that the number of cards remaining in your library at the time Thassa's Oracle's enter-the-battlefield ability will check is N (commonly N = 5).

Step 4

Get Thassa's Oracle onto the battlefield (cast it, reanimate it, etc.). When it enters the battlefield its triggered ability will trigger and then later resolve; when that triggered ability resolves it uses your current devotion to blue to compute X (devotion counts in the mana costs of permanents you control, including Thassa's Oracle, per Ruling [2020-01-24]).

Step 5

If X (your devotion to blue at that time) is greater than or equal to the number of cards in your library, Thassa's Oracle's ability states you win the game (this is Oracle's printed oracle text). If that condition is met when the trigger resolves, you win.

Resolution

After Doomsday resolves your library will contain only the chosen cards (subject to the search rules [701.15d] and the fewer-than-five ruling [Ruling [2018-03-16]]). If Thassa's Oracle enters the battlefield while your devotion to blue (counting mana symbols in the mana costs of permanents you control, including the Oracle) is greater than or equal to the current number of cards in your library, you win the game due to its enter-the-battlefield ability (Thassa's Oracle oracle text; Ruling [2020-01-24]; [701.15d]; Ruling [2018-03-16]).