Doomsday Excruciator enters the battlefield, it triggers, exiling all but the bottom six cards of each library face down.
Activate a creature you control by tapping it, causing an opponent to mill cards equal to the creature's toughness.
Repeat step 3 as desired and/or able.
Notes
If an opponent has zero cards in their library as they begin their turn, they will lose the game during their draw step due to attempting to draw from an empty library. Depending on how many creatures you have available, it is possible to cause multiple or all opponents to lose the game in this fashion.
Results
Near-infinite mill.
Near-infinite self-mill.
Metadata
Bracket tag
SpicyBracket 3-4+
Probably 3 or 4, but hard to classify
1
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3
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5
1 · Exhibition5 · cEDH
Bracket tags are estimated from the cards and results of each combo, as a guideline rather than a strict classification.