Activate Krark-Clan Ironworks by sacrificing Mister Gutsy, adding {C}{C}.
When Mister Gutsy dies, its second ability and Nim Deathmantle trigger.
Resolve the Mister Gutsy trigger, creating a number of Junk tokens equal to the number of +1/+1 counters that were on it.
If you created a Junk token, activate Krark-Clan Ironworks by sacrificing a Junk, adding {C}{C}.
Resolve the Nim Deathmantle trigger, causing you to pay {4} to return Mister Gutsy from your graveyard to the battlefield with a +1/+1 counter on it, and attaching Nim Deathmantle to it.
Repeat.

Infinite LTB

Infinite ETB

Infinite sacrifice triggers

Infinite death triggers

Mister Gutsy

Nim Deathmantle

Krark-Clan Ironworks

Metallic Mimic

Activate Krark-Clan Ironworks by sacrificing Mister Gutsy, adding {C}{C}.
When Mister Gutsy dies, its second ability and Nim Deathmantle trigger.
Resolve the Mister Gutsy trigger, creating a number of Junk tokens equal to the number of +1/+1 counters that were on it.
If you created a Junk token, activate Krark-Clan Ironworks by sacrificing a Junk, adding {C}{C}.
Resolve the Nim Deathmantle trigger, causing you to pay {4} to return Mister Gutsy from your graveyard to the battlefield, and attaching Nim Deathmantle to it.
When Mister Gutsy enters the battlefield, Surrak and Goreclaw triggers, putting a +1/+1 counter on Mister Gutsy.
Repeat.

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