War of the Spark and Modern Horizons rank among the most impactful sets in the history of the format. To highlight this, here is a quick overview of the ten most-played new cards from these sets among the 457 decklists submitted for Mythic Championship IV.
Total number of copies: 422, all maindeck.
Hogaak is Modern Horizon's most important addition to the format. As it turns out, zero-mana 8/8 tramplers that can be cast as early as turn two and that can just be replayed from the graveyard are pretty powerful. Hogaak does require you to craft your deck around it, and it is vulnerable to anti-graveyard cards, but it is namesake card of the most-played deck in the room. It is even seeing a small amount of play in Dredge decks.
Total number of copies: 379, all maindeck.
Carrion Feeder can convoke Hogaak, trigger Stitcher's Supplier, and eventually grow into a huge threat. Especially when you can keep sacrificing creatures like Bloodghast, Gravecrawler, and Vengevine that return from the graveyard. Carrion Feeder is even a Zombie for Gravecrawler! Given all this, it's one of the key pieces of the new Hogaak deck.
Total number of copies: 260, divided between 259 main deck copies and 1 sideboard copy.
Karn, the Great Creator is War of the Spark's most important addition to Modern. Karn can fetch such cards as Mycosynth Lattice for an instant win on an empty board, Ensnaring Bridge to lock down attackers, or Grafdigger's Cage to stop graveyard recursion. While Karn has found a home in a variety of decks, it is arguably at its best when you can ramp into Mycosynth Lattice with Urza's Mine, Urza's Power Plant, and Urza's Tower.
Total number of copies: 229, divided between 118 main deck copies and 111 sideboard copies.
Force of Negation is a nice callback to Force of Will, and it helps to keep combo decks like Neoform in check. Many White-Blue Control decks play several copies in their main deck as it fits their game plan and helps them protect a planeswalker. But it also works as a solid sideboard card in a variety of archetypes.
Total number of copies: 227, split between 13 main deck and 214 sideboard.
There are several tribal decks in Modern. Humans is the most notable one, but there is also Spirits, Merfolk, and Goblins, and so on. Against these decks, Plague Engineer is an excellent sideboard card. And given that it's never truly dead in any matchup—a 2/2 deathtouch is always serviceable—it's an acceptable card to put in your main deck if you want to free up additional sideboard slots.
Total number of copies: 146, split between 118 main deck and 28 sideboard.
In a format where card draw spells like Faithless Looting and Serum Visions are quite popular, the static ability on Narset is very strong. What's more, you effectively get a Dig Through Time, so it's not surprising that many White-Blue Control decks have adopted the planeswalker in their main decks.
Total number of copies: 145, all sideboard.
Artifact-based decks like Affinity and Hardened Scales, which did well at Mythic Championship II in London several months ago, have fallen out of favor nowadays. One of the reasons are the newly printed anti-artifact cards. Taking out both Arcbound Ravager and Steel Overseer for zero mana is simply unfair. What's more, Force of Vigor is also excellent against Leyline of the Void, Ensnaring Bridge, Chalice of the Void, Blood Moon, etcetera.
Total number of copies: 132, split between 129 main deck and 3 sideboard.
Blast Zone is a mana base upgrade for colorless decks like Eldrazi Tron. The land can sweep up a large part of the board, and it doesn't cost any spell slots to include it in your deck.
Total number of copies: 126, all main deck.
Wrenn and Six does it all. It answers Noble Hierarch and Champion of the Parish. It returns Bloodstained Mire to help hit your land drops or to break the discard symmetry on Liliana of the Veil. It returns Nurturing Peatland to help you grind in a long game. And the threat of its ultimate demands an answer from control players. All in all, Wrenn and Six is a great reason to leave behind The Rock and to pick up Jund.
Total number of copies: 120, split between 105 main deck and 15 sideboard.
Teferi, Time Raveler says "no" to casting spells outside of sorcery speed, which not only stops countermagic but also nullifies Bring to Light, Finale of Promise, Bloodbraid Elf's cascade, and Rift Bolt's suspend. And as we've seen in Standard, simply using Teferi as a cantrip bounce spell is effective too. Many White-Blue Control players in particular have added a few copies of Teferi, Time Raveler.
That concludes my overview of the ten most-played Modern cards at Mythic Championship IV from the latest three sets. Overall, the impact of Modern Horizons and War of the Spark has been massive.
Core Set 2020 has not had a huge impact yet. The most-played card from that set is Veil of Summer, at 34 copies. But it's all still very fresh, and new gems may be found in the coming months.