Cast Doomsday Excruciator by paying {B}{B}{B}{B}{B}{B}.
When Doomsday Excruciator enters the battlefield, it triggers, exiling all but the bottom six cards of each library face down.
Cast Breach the Multiverse by paying {5}{B}{B}, causing each player to mill ten cards, thus milling the remainder of each player's library.
When your opponents go to draw a card during their next draw steps, they will lose the game due to attempting to draw from an empty library.

Infinite mill

Infinite self-mill

Doomsday Excruciator

Breach the Multiverse

Cast Doomsday Excruciator by paying {B}{B}{B}{B}{B}{B}.
When Doomsday Excruciator enters, it triggers, causing each player to exile all but the bottom six cards of their library.
Cast Maddening Cacophony by paying {1}{U}, causing each opponent to mill the rest of their library.

Near-infinite self-mill

Maddening Cacophony

Cast Doomsday Excruciator by paying {B}{B}{B}{B}{B}{B}.
When Doomsday Excruciator enters, it triggers, causing each player to exile all but the bottom six cards of their library.
Cast Fractured Sanity by paying {U}{U}{U}, causing each opponent to mill the rest of their library.

Fractured Sanity

Cast Doomsday Excruciator by paying {B}{B}{B}{B}{B}{B}.
When 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.

Near-infinite mill

Phenax, God of Deception

Cast Doomsday Excruciator by paying {B}{B}{B}{B}{B}{B}.
When Doomsday Excruciator enters the battlefield, it triggers, exiling all but the bottom six cards of each player's library.
Activate Rakdos by sacrificing Doomsday Excruciator.
When Doomsday Excruciator dies, Rakdos's first ability triggers, exiling the top six cards of an opponent's library.
When the opponent targeted in step 4 would draw a card during their next draw step, they will instead lose the game due to having zero cards in their library.

Each opponent loses the game

Exile each opponent's library

Rakdos, the Muscle

Cast Doomsday Excruciator by paying six {B}.
When Doomsday Excruciator enters the battlefield, it triggers, causing each player to exile all but the bottom six cards of their library.
Cast Thassa's Oracle by paying {U}{U}.
When Thassa's Oracle enters the battlefield, it triggers, causing you to win the game.

Win the game

Thassa's Oracle

Cast Doomsday Excruciator by paying {B}{B}{B}{B}{B}{B}.
When Doomsday Excruciator enters, it triggers, causing each player to exile all but the bottom six cards of their library.
Cast One Ring to Rule Them All by paying {2}{B}{B}.
When One Ring to Rule Them All enters, its first chapter ability triggers, causing Doomsday Excruciator to become your Ring-bearer and causing each opponent to mill the rest of their library.

One Ring to Rule Them All

Cast Doomsday Excruciator by paying six {B}.
When Doomsday Excruciator enters the battlefield, it triggers, exiling all but the bottom six cards of each library.
Cast Shared Trauma by paying {B}, and then choosing to pay an additional {6}, milling the remainder of each library.
Move to the next opponent's turn, causing them to lose the game due to attempting to draw from an empty library.
Repeat step 4 for each remaining opponent.

Shared Trauma

Cast Doomsday Excruciator by paying {B}{B}{B}{B}{B}{B}. When it enters, it triggers, exiling all but the bottom six cards of each library.
Activate Memory Vessel by tapping and exiling it, exiling the remainder of each library.
Each opponent will lose the game during their next draw step due to attempting to draw from an empty library.

Combos with "Doomsday Excruciator"