Smaug the Impenetrable + Metalwork Colossus + Primal Vigor + Goblin Bombardment

Smaug the Impenetrable

Metalwork Colossus

Primal Vigor

Goblin Bombardment

How it works

1. Activate Goblin Bombardment by sacrificing Metalwork Colossus, dealing 1 damage to Smaug.
2. Smaug triggers, creating two artifact tokens due to Primal Vigor.
3. Activate Metalwork Colossus by sacrificing the two artifact tokens, returning Metalwork Colossus from your graveyard to your hand.
4. Cast Metalwork Colossus by paying 0.
5. Repeat.

This infinite loop relies on the brilliant synergy between Goblin Bombardment, Smaug the Impenetrable, Primal Vigor, and Metalwork Colossus to generate endless sacrifice and damage triggers. You start by using Goblin Bombardment to fling Metalwork Colossus right at Smaug the Impenetrable, dealing the 1 noncombat damage needed to trigger Smaug's ability. Because Primal Vigor doubles token creation, taking that damage turns into four newly minted Treasure tokens instead of just two. You then feed two of those fresh tokens back into Metalwork Colossus to pull it straight out of your graveyard and back into your hand, where its mana reduction lets you recast it for free.