There are a number of artifacts and planeswalkers in Standard right now that have synergy. The shells range wildly, and we’ve seen what Team CFB came up with at the last Pro Tour with a U/G Karn shell. How about W/B?
Karn, Scion of Urza is the centerpiece of these decks. A 4-mana planeswalker with a decently high loyalty is above the curve and Karn has an immediate impact. In a deck with a bunch of artifacts, the -2 can present a formidable threat. Making a 3/3 on the first turn that will only grow greatly diminishes their ability to threaten Karn. There will also be plenty of opportunities where you don’t need Karnstructs and can instead start cashing in for card advantage. The +1 is very likely to deliver a land, but you’ll be able to draw the good stuff with a minus later.
There are already a high number of powerful Constructs in Standard right now, and it just so happens that Metallic Mimic combos well with them. While 1-toughness creatures aren’t exactly where you want to be against Goblin Chainwhirler, the ability to pump the rest of your team is quite powerful. You also have plenty of recursion to get your Mimics back.
Scrap Trawler is another Construct that really shines in this deck. Creatures die in Standard. It’s just something that happens. The format revolves around combat or removing threats, and having the Trawler to start getting these cards back from the graveyard is a powerful card advantage engine that we also saw featured in the U/G versions.
Ballista is another Construct that happens to combo well with Mimic, but it does much more. It’s a great early game play to control the board and it’s a great late game spell to either establish control or just end the game. The fact that you’re playing the full playset of Scrap Trawlers to complement your Ballistas means that you’re not afraid of using or losing them early. Any artifact going to your graveyard will get the Ballista back, and since you can always remove counters from Ballista in response to an exile effect like Vraska’s Contempt or Cast Out means that they’ll always be ready for more.
Your final Construct is Foundry Inspector. A 3/2 for 3 isn’t the worst for an aggressive deck, but it combines with Mimic to get bigger, makes Ballista and everything Scrap Trawler returns cheaper. It’s also the perfect size to crew your Heart of Kirans.
Heart of Kiran provides an evasive threat that can naturally be crewed by your 3-drop Inspectors and Trawlers. Having multiple angles to attack from makes things hard for your opponents to defend, and incidental damage in a Ballista deck adds up quickly. A couple of Aethersphere Harvesters complement the Hearts as a way to use your smaller creatures later in the game and to gain some important life.
Toolcraft Exemplar isn’t the baddest creature on the block anymore thanks to Chainwhirler, but a 3-power creature for 1 mana can still get in real damage. Not every deck plays Chainwhirler, and not every Chainwhirler deck always has it or can cast it on turn 3, so getting in a couple of hits or crewing a Heart is quite nice.
Teshar, Ancestor’s Apostle doesn’t combo super well with Walking Ballista unless you already have a Mimic in play, but it does work well with the rest of your deck. A 2/2 for 4, even with flying, is pretty far below the curve, but you’re playing almost all historic spells and many are cheap, so this can allow you to effectively “go off.” Chaining 1- and 0-mana artifacts into bringing Scrap Trawlers back into returning these artifacts can present an insane engine even without the help of a Foundry Inspector!
Renegade Map is at its best here. It’s a cheap historic spell and an artifact you can send to your graveyard at any time with Scrap Trawler to bring back Walking Ballista. The fact that it fixes your mana is just icing on the cake.
The Construct package built around Karn presents some incredible board states and has plenty of aggression to beat even the decks working hard to beat you. You’re a little light on interaction game 1 if you fall behind with only Fatal Pushes and the Ballistas, but having access to white and black means a lot of great sideboard options for an already powerful shell!