Activate Throne of Geth by tapping it and sacrificing Ugin's Nexus.
Ugin's Nexus is exiled instead of being put into your graveyard, causing you to take an extra turn after this one.
Resolve the Throne of Geth ability, putting a loyalty counter on Karn.
Activate Karn's second loyalty ability by removing two loyalty counters from it, returning Ugin's Nexus from exile to your hand.
Move to your next turn.
Cast Ugin's Nexus by paying {5}.
Flux Channeler triggers, putting a loyalty counter on Karn.
Repeat.

Infinite turns

Lock

Karn, the Great Creator

Ugin's Nexus

Throne of Geth

Flux Channeler

Cast Sol Ring by paying its mana cost.
When you cast that spell, Flux Channeler triggers, putting one +1/+1 counter on Arcbound Reclaimer and at least two additional artifacts you control.
Activate Sol Ring by tapping it, adding mana.
Activate Krark-Clan Ironworks by sacrificing Sol Ring, adding {C}{C}.
Activate Arcbound Reclaimer by removing a +1/+1 counter from it, putting Sol Ring from your graveyard on top of your library.
Activate Iron Spider's last ability by paying {2} and removing two +1/+1 counters from artifacts you control, drawing Sol Ring.
Repeat.

Infinite colorless mana

Infinite draw triggers

Infinite proliferate

Infinite storm count

Infinite artifact ETB

Infinite artifact LTB

Infinite artifact sacrifice triggers

Arcbound Reclaimer

Iron Spider, Stark Upgrade

Krark-Clan Ironworks

Sol Ring

Combos with "Flux Channeler"