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

Three Steps Ahead

Cast Three Steps Ahead by paying {3}{U}, creating 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 2.

Infinite colorless mana

Roxanne, Starfall Savant

Basalt Monolith

Cast Three Steps Ahead by paying its mana cost, creating 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 2.

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 Sea Gate Stormcaller by paying {1}{U}.
When Sea Gate Stormcaller enters the battlefield, it triggers, copying the next instant or sorcery spell you cast this turn with mana value 2 or less.
Cast Three Steps Ahead by paying {U} plus an additional {3} to select its second mode, targeting Sea Gate Stormcaller.
Sea Gate Stormcaller and Storm-Kiln Artist trigger.
Resolve the Storm-Kiln Artist trigger, creating a Treasure token.
Resolve the Sea Gate Stormcaller trigger, copying Three Steps Ahead, with the copy targeting Sea Gate Stormcaller.
Storm-Kiln Artist triggers, creating a Treasure token.
Resolve the copy of Three Steps Ahead, creating a token copy of Sea Gate Stormcaller with haste.
When the token Sea Gate Stormcaller enters the battlefield, it triggers, copying the next instant or sorcery spell you cast this turn with mana value 2 or less.
Holding priority, activate two Treasures by tapping and sacrificing them, adding {U}{U}.
Cast Narset's Reversal by paying {U}{U}, targeting Three Steps Ahead.
Sea Gate Stormcaller and Storm-Kiln Artist trigger.
Resolve the Storm-Kiln Artist trigger, creating a Treasure token.
Resolve the Sea Gate Stormcaller trigger, copying Narset's Reversal, with the copy targeting the original Narset's Reversal.
Storm-Kiln Artist triggers, creating a Treasure token.
Resolve the copy of Narset's Reversal, returning the original Narset's Reversal to your hand and creating a copy of Narset's Reversal targeting Three Steps Ahead.
Storm-Kiln Artist triggers, creating a Treasure token.
Resolve the Narset's Reversal copy, returning Three Steps Ahead to your hand and creating a copy of Three Steps Ahead targeting Sea Gate Stormcaller.
Storm-Kiln Artist triggers, creating a Treasure token.
Resolve the Three Steps Ahead copy, creating a token copy of Sea Gate Stormcaller with haste.
When the token Sea Gate Stormcaller enters the battlefield, it triggers, copying the next instant or sorcery spell you cast this turn with mana value 2 or less.
Activate four Treasures by tapping and sacrificing them, adding {3}{U}.
Repeat from step 3.

Infinite magecraft triggers

Storm-Kiln Artist

Sea Gate Stormcaller

Narset's Reversal

Combos with "Three Steps Ahead"