Create a copy of Worldwalker Helm, which will also create a Map token.
Activate Urza's first ability by tapping a Worldwaker Helm and a Map, adding {U}{U}.
Activate a Worldwalker Helm by paying {1}{U} and tapping it, creating a token copy of the Worldwalker Helm token and a Map token for each Worldwalker Helm you control.
Activate Urza's first ability twice by tapping two Maps, adding {U}{U}.
Repeat from step 3.

Infinite blue mana

Exile your library

Cast all cards in your library without paying their mana costs

Infinite Map tokens

Urza, Lord High Artificer

Worldwalker Helm

Replication Specialist

Cast Ugin's Nexus by paying {5}.
Ugin's Nexus enters the battlefield, triggering Replication Specialist, causing you to pay {1}{U} to create a copy of Ugin's Nexus.
Exile the token copy of Ugin's Nexus due to the legend rule, causing you to take an extra turn after this one.
Activate Master Transmuter by paying {U}, tapping it, and returning Ugin's Nexus to your hand, choosing not to put an artifact card from your hand onto the battlefield.
Repeat each turn.

Infinite turns

Master Transmuter

Ugin's Nexus

Cast Silver Myr by paying {2}.
Silver Myr enters the battlefield, triggering Replication Specialist, causing you to pay {1}{U} to create a token copy of Silver Myr.
Activate Lightning Greaves' equip ability by paying {0}, attaching it to a Silver Myr.
Activate the Silver Myr by tapping it, adding {U}.
Repeat from step 3 one additional time.
Cast Myr Galvanizer by paying {3}.
Myr Galvanizer enters the battlefield, triggering Replication Specialist, causing you to pay {1}{U} to create a token copy of Myr Galvanizer.
Activate Lightning Greaves' equip ability by paying {0}, attaching it to a Myr Galvanizer.
Activate the Myr Galvanizer by paying {1} and tapping it, untapping all other Myr you control.
Activate Lightning Greaves' equip ability by paying {0}, attaching it to a Silver Myr.
Activate the Silver Myr by tapping it, adding {U}.
Repeat from step 10 one additional time.
Repeat from step 8.

Infinite untap of Myr you control

Myr Galvanizer

Silver Myr

Lightning Greaves

Cast Silver Myr by paying {2}.
Silver Myr enters the battlefield, triggering Replication Specialist, causing you to pay {1}{U} to create a token copy of Silver Myr.
Activate both Silver Myr by tapping them, adding {U}{U}.
Cast Myr Galvanizer by paying {3}.
Myr Galvanizer enters the battlefield, triggering Replication Specialist, causing you to pay {1}{U} to create a token copy of Myr Galvanizer.
Activate a Myr Galvanizer by paying {1} and tapping it, untapping all other Myr you control.
Activate both Silver Myr by tapping them, adding {U}{U}.
Repeat from step 6.

Thousand-Year Elixir

Activate Abuelo by paying {1}{W}{U}, exiling Ugin's Nexus until the beginning of the next end step.
At the beginning of your end step, Abuelo triggers, returning Ugin's Nexus from exile to the battlefield.
When Ugin's Nexus enters the battlefield, Replication Specialist triggers, causing you to pay {1}{U} to create a token copy of Ugin's Nexus.
Put the token Ugin's Nexus into exile due to the legend rule and its replacement effect, causing you to take an extra turn after this one.
Activate Abuelo by paying {1}{W}{U}, exiling Ugin's Nexus until the beginning of the next end step.
Move to your next turn, not skipping it as Ugin's Nexus is not on the battlefield.
Repeat from step 2.

Abuelo, Ancestral Echo

Cast Genesis Chamber by paying {2}.
When Genesis Chamber enters the battlefield, Replication Specialist triggers, causing you to pay {1}{U} to create a token copy of Genesis Chamber.
Cast Emry from the command zone by paying {U}.
When Emry enters the battlefield, it and both Genesis Chambers trigger.
Resolve the Emry trigger, causing you to mill four cards.
Resolve both Genesis Chamber triggers, creating two 1/1 Myr artifact creature tokens.
Activate Phyrexian Altar by sacrificing Emry, adding {U}.
Choose to return Emry to the command zone from your graveyard.
Repeat from step 3.

Infinite LTB

Infinite ETB

Infinite colored mana

Infinite sacrifice triggers

Infinite death triggers

Infinite storm count

Infinite creature tokens

Infinite commander casts

Infinite self-mill

Emry, Lurker of the Loch

Phyrexian Altar

Genesis Chamber

Cast Guardians of Koilos by paying {5}.
When Guardians of Koilos enters the battlefield, it and Replication Specialist trigger.
Resolve the Replication Specialist trigger, causing you to pay {1}{U} to create a token copy of Guardians of Koilos.
When the token Guardians of Koilos enters the battlefield, it triggers.
Resolve both Guardians of Koilos triggers, choosing to return nothing to your hand from the battlefield.
Cast Dutiful Replicator by paying {3}.
When Dutiful Replicator enters the battlefield, it and Replication Specialist trigger.
Holding priority, activate a mana-producing artifact by tapping it, adding at least {U}.
Resolve the Replication Specialist trigger, causing you to pay {1}{U} to create a token copy of Dutiful Replicator.
When the token Dutiful Replicator enters the battlefield, it triggers, causing you to pay {1} to create a token copy of the Guardians of Koilos token.
When the Guardians of Koilos token enters the battlefield, it triggers, choose to return nothing to your hand from the battlefield.
Activate Krark-Clan Ironworks by sacrificing the Dutiful Replicator token and the Guardians of Koilos token, adding {C}{C}{C}{C}.
When the tokens die, Dross Scorpion triggers twice.
Resolve the first trigger, untapping the mana-producing artifact.
Activate the artifact by tapping it, adding at least {U}.
Repeat steps 14 and 15 one additional time.
Resolve the nontoken Dutiful Replicator trigger from step 7, causing you to pay {1} to create a token copy of Guardians of Koilos.
When the Guardians of Koilos token enters the battlefield, it triggers, returning the nontoken Dutiful Replicator from the battlefield to your hand.
Activate Krark-Clan Ironworks by sacrificing the Guardians of Koilos token, adding {C}{C}.
When the token dies, Dross Scorpion triggers, untapping the mana-producing artifact.
Repeat from step 6.
Once you have infinite blue and/or colorless mana, you may forego sacrificing the creature tokens.

Infinite colorless mana

Guardians of Koilos

Dross Scorpion

Dutiful Replicator

Krark-Clan Ironworks

Cast Guardians of Koilos by paying {5}.
When Guardians of Koilos enters the battlefield, it and Replication Specialist trigger.
Resolve the Replication Specialist trigger, causing you to pay {1}{U} to create a token copy of Guardians of Koilos.
When the token Guardians of Koilos enters the battlefield, it triggers.
Resolve both Guardians of Koilos triggers, choosing to return nothing to your hand from the battlefield.
Cast Dutiful Replicator by paying {3}.
When Dutiful Replicator enters the battlefield, it and Replication Specialist trigger.
Holding priority, activate a mana-producing artifact by tapping it, adding at least {U}.
Resolve the Replication Specialist trigger, causing you to pay {1}{U} to create a token copy of Dutiful Replicator.
When the token Dutiful Replicator enters the battlefield, it triggers, causing you to pay {1} to create a token copy of the Guardians of Koilos token.
When the Guardians of Koilos token enters the battlefield, it triggers, choose to return nothing to your hand from the battlefield.
Activate Ashnod's Altar by sacrificing the Dutiful Replicator token and the Guardians of Koilos token, adding {C}{C}{C}{C}.
When the tokens die, Dross Scorpion triggers twice.
Resolve the first trigger, untapping the mana-producing artifact.
Activate the artifact by tapping it, adding at least {U}.
Repeat steps 14 and 15 one additional time.
Resolve the nontoken Dutiful Replicator trigger from step 7, causing you to pay {1} to create a token copy of Guardians of Koilos.
When the Guardians of Koilos token enters the battlefield, it triggers, returning the nontoken Dutiful Replicator from the battlefield to your hand.
Activate Ashnod's Altar by sacrificing the Guardians of Koilos token, adding {C}{C}.
When the token dies, Dross Scorpion triggers, untapping the mana-producing artifact.
Repeat from step 6.
Once you have infinite blue and/or colorless mana, you may forego sacrificing the creature tokens.

Ashnod's Altar

Cast Ugin's Nexus by paying {5}.
When Ugin's Nexus enters the battlefield, Replication Specialist triggers, causing you to pay {1}{U} to create a token copy of Ugin's Nexus.
Put the token Ugin's Nexus into exile due to the legend rule and the token's replacement effect, causing you to take an extra turn after this one.
At the beginning of your end step, Phenomenon Investigators triggers, returning Ugin's Nexus from the battlefield to your hand and causing you to draw a card.
Repeat during each of your turns.

Phenomenon Investigators

Cast Basalt Monolith by paying {3}.
When Basalt Monolith enters the battlefield, Replication Specialist triggers, causing you to pay {1}{U} to create a token copy of Basalt Monolith.
Activate the token Basalt Monolith's first ability by tapping it, adding {C}{C}{C}.
Roxanne's second ability triggers, adding {C}.
Activate the token Basalt Monolith's second ability by paying {3}, untapping it.
Repeat from step 3.

Combos with "Replication Specialist"