At the beginning of your end step, The Fifth Doctor triggers.
Holding priority, activate mana-producing creatures you control by tapping them, adding at least {2}{U}.
Activate Adric's first ability by paying {2}{U} and tapping them, copying the Fifth Doctor's trigger.
Resolve the copied triggered ability, untapping all creatures you control that didn't enter or attack this turn and putting a +1/+1 counter on each them.
Repeat from 2.

Infinite +1/+1 counters on all creatures you control except ones that attacked or entered the battlefield this turn

Infinite mana creatures you control can produce except ones that attacked or entered the battlefield this turn

Infinite untap of creatures you control except ones that attacked or entered the battlefield this turn

The Fifth Doctor

Adric, Mathematical Genius

Deal combat damage to an opponent using Etrata, triggering its ability.
Holding priority, activate Adric and Strionic Resonator by paying {4}{U} and tapping them, copying Etrata's trigger twice.
Resolve all Etrata triggers, exiling three creatures an opponent controls and putting hit counters on them, and then causing that opponent to lose the game.

Target opponent loses the game

Etrata, the Silencer

Strionic Resonator

Deal combat damage to an opponent using Etrata, triggering its ability twice due to Roaming Throne.
Holding priority, activate Adric by paying {2}{U} and tapping it, copying either of Etrata's triggers.
Resolve all Etrata triggers, exiling three creatures an opponent controls and putting hit counters on them, and then causing that opponent to lose the game.

Roaming Throne

Activate Ioreth's second ability by tapping it, targeting Adric and Selvala.
Holding priority, activate Selvala by paying {G} and tapping it, adding at least {3}{G}{U}.
Activate Adric by paying {2}{U} and tapping it, copying Ioreth's ability, with the copy targeting Selvala and Adric.
Resolve the copy of Ioreth's ability, untapping Adric and Selvala.
Repeat from step 2.

Infinite colored mana

Infinite untap of legendary creatures you control

Infinite mana legendary creatures you control can produce

Selvala, Heart of the Wilds

Ioreth of the Healing House

At the beginning of your upkeep, Progenitor Mimic triggers.
Holding priority, activate Adric by paying {2}{U} and tapping it, copying Progenitor Mimic's trigger.
Resolve both triggers, creating two token copies of Biovisionary.
At the beginning of your end step, each Biovisionary triggers.
Resolve the first trigger, causing you to win the game.

Win the game

Biovisionary

Progenitor Mimic

Cast Writhing Chrysalis by paying {2}{R}{G}.
Writhing Chrysalis and Ulalek trigger.
Holding priority, activate Adric's first ability by paying {2}{U} and tapping it, copying Ulalek's trigger.
Resolve the copied Ulalek trigger, causing you to pay {C}{C} and creating a copy of the Writhing Chrysalis spell, Writhing Chrysalis's trigger, and Ulalek's trigger.
Resolve the copied Ulalek trigger, causing you to pay {C}{C} and creating a copy of at least two Writhing Chrysalis spells, at least two Writhing Chrysalis's triggers, and Ulalek's trigger.
Resolve a Writhing Chrysalis trigger, creating two Eldrazi Spawn tokens.
Activate two Eldrazi Spawn tokens by sacrificing them, adding {C}{C}.
Repeat from 5 any number of times.
Once you have infinite copies of the spells and triggers, you can resolve them all, activate any number of Eldrazi Spawn tokens, and trigger all Writhing Chrysalis's final abilities.

Infinite LTB

Infinite ETB

Infinite sacrifice triggers

Infinite death triggers

Infinite colorless mana

Infinite creature tokens

Infinite +1/+1 counters on Writhing Chrysalises

Ulalek, Fused Atrocity

Writhing Chrysalis

Deal combat damage to an opponent using the creature that has Biorganic Carapace attached, triggering it.
Holding priority, activate Adric by paying {2}{U} and tapping it, copying the creature's trigger.
Resolve the copy of the creature's ability, drawing a card for each modified creature you control.
Holding priority, activate Mind Over Matter by discarding a card, untapping Adric.
Activate Mind Over Matter by discarding a card, untapping a mana-producing permanent.
Activate the mana-producing permanent by tapping it, adding {U}.
Repeat from step 5 two additional times.
Repeat from step 2.

Infinite self-discard triggers

Infinite draw triggers

Infinite looting

Near-infinite card draw

Near-infinite untap of permanents you control

Near-infinite mana permanents you control can produce

Biorganic Carapace

Mind Over Matter

Activate any number of permanents by tapping them, adding at least {4}{U}{R}.
Activate Feldon by paying {2}{R} and tapping it, targeting Worldgorger Dragon.
Activate Adric by paying {2}{U} and tapping it, copying Feldon's ability targeting Worldgorger Dragon.
Resolve the copy of Feldon's ability, creating a token copy of Worldgorger Dragon.
When the Worldgorger Dragon token enters, its first ability triggers, exiling all other permanents you control.
Resolve the Feldon ability from step 2, creating a token copy of Worldgorger Dragon.
When the Worldgorger Dragon token enters, its first ability triggers, exiling all other permanents you control.
When the Worldgorger Dragon token created in step 4 leaves the battlefield, its second ability triggers, returning all cards exiled with it to the battlefield.
Repeat.

Infinite landfall triggers

Infinite blinking of permanents you control

Infinite mana permanents you control that enter the battlefield untapped can produce

Feldon of the Third Path

Worldgorger Dragon

Thousand-Year Elixir

Combos with "Adric, Mathematical Genius"