Matt Nass has won two Grand Prix with his take on Krark-Clan Ironworks combo in Modern, but that doesn't mean that there's only one way to build the deck. The core of the combo is the same in each build, but there are a myriad of ways to close out the game and customize your deck to interact with the decks you expect to face. Let's take a look:

Krark-Clan Ironworks - Modern | Tabodon, Modern Challenge 15th Place

• Creatures (6)
• 1 Myr Retriever
• 1 Walking Ballista
• 4 Scrap Trawler

• Sorceries (4)
• 4 Ancient Stirrings

• Artifacts (32)
• 2 Pyrite Spellbomb
• 3 Chromatic Sphere
• 3 Engineered Explosives
• 4 Chromatic Star
• 4 Ichor Wellspring
• 4 Krark-Clan Ironworks
• 4 Mind Stone
• 4 Mox Opal
• 4 Terrarion

• Lands (18)
• 2 Forest
• 2 Aether Hub
• 3 Buried Ruin
• 3 Inventors' Fair
• 4 Darksteel Citadel
• 4 Grove of the Burnwillows

• Sideboard (15)
• 2 Defense Grid
• 3 Galvanic Blast
• 2 Ghirapur Aether Grid
• 2 Guttural Response
• 4 Nature's Claim
• 2 Wurmcoil Engine

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The biggest question for this deck is how exactly you want to win the game. Matt Nass has said that anything outside of Pyrite Spellbomb isn't necessary, and will lead to dead draws. The Pyrite Spellbomb combo involves declaring your intention to cast a spell, and sacrificing both Scrap Trawler and Myr Retriever at the same time to pay for the card. This lets you get back Scrap Trawler with Myr Retriever's trigger, and both Pyrite Spellbomb and Myr Retriever with Scrap Trawler triggers. Sacrificing your Pyrite Spellbomb lets you rebuy Mox Opal to continue generating enough Red mana to kill your opponent.

That said, there are other options that make your life a little easier, particularly on Magic Online, where click-intensive combos can be tedious and lead to timeouts. Some builds opt to play cards like Wurmcoil Engine or Emrakul, the Aeons Torn as alternate ways to end the game. This build opts instead to play a single Walking Ballista. This is a card that can come down early to disrupt opposing mana creatures or creature lands, but is also a mana sink that can just kill your opponent on the spot if you can generate enough mana.

If you're looking for a new combo deck in Modern, this deck has proven itself to be fast enough to keep pace with even the most explosive combo decks. It's also shown that Scrap Trawler is an incredible value engine that can let you grind through both aggressive starts or disruption. Why choose between a deck that can win quickly or through disruption when you can choose to play a deck that can do both?