Cast Maddening Cacophony with kicker by paying {4}{U}{U}, causing each opponent to mill half their library, rounded up.
Activate Consuming Aberration by tapping it, causing a opponent to mill cards equal to the cards in opponents' graveyards, milling the remainder of their library.

Infinite mill for target opponent

Near-infinite mill

Phenax, God of Deception

Consuming Aberration

Maddening Cacophony

Cast Maddening Cacophony with kicker by paying {4}{U}{U}, causing the opponent named by Sewer Nemesis to mill half their library, rounded up.
Activate Sewer Nemesis by tapping it, causing the opponent to mill cards equal to the cards in their graveyard, milling the remainder of their library.

Sewer Nemesis

Activate Eater of the Dead by tapping it, causing a player to mill cards equal to its toughness.
Activate Eater of the Dead by paying {0}, exiling a creature card from a graveyard and untapping Eater of the Dead.
Repeat as able.

Near-infinite self-mill

Eater of the Dead

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.

Doomsday Excruciator

Activate a creature you control by tapping it, causing a player to mill cards equal to that creature's toughness.
If a creature card was milled this way, Zellix triggers, creating a 1/1 Horror creature token.
If a Horror entered, Intruder Alarm triggers, untapping all creatures.
Repeat.

Near-infinite creature tokens

Near-infinite untap of all creatures

Near infinite ETB

Zellix, Sanity Flayer

Intruder Alarm

Activate all creatures you control by tapping them.
Resolve the first creature's ability, causing target opponent to mill cards equal to the creature's toughness.
For each creature card milled this way, Undead Alchemist triggers, exiling that card and causing you to create a 2/2 Zombie creature token.
If a Zombie is created, it enters the battlefield, triggering Intruder Alarm, untapping all creatures.
Repeat from step 2 for each remaining trigger.
Repeat from step 1.

Infinite mill

Near-infinite ETB

Undead Alchemist

Activate King Macar by tapping it, causing a player to mill cards equal to King Macar's toughness.
Activate Freed from the Real by paying {U}, untapping King Macar.
King Macar triggers, exiling any opposing creature and creating a Gold token.
Activate the Gold token by sacrificing it, adding {U}.
Repeat.

Exile all of your opponents' creatures

Freed from the Real

King Macar, the Gold-Cursed

Activate King Macar by tapping it, causing a player to mill cards equal to King Macar's toughness.
Activate Pemmin's Aura by paying {U}, untapping King Macar.
King Macar triggers, exiling any opposing creature and creating a Gold token.
Activate the Gold token by sacrificing it, adding {U}.
Repeat.

Pemmin's Aura

Activate The Walls of Ba Sing Se by tapping it, causing a player to mill thirty cards.
Activate Freed from the Real by paying {U}, untapping The Walls of Ba Sing Se.
Repeat as mana allows.

Combos with "Phenax, God of Deception"