haven't featured a deck with Karn for a while, so I figured it was time to rectify that grievous oversight. Of course, this particular Karn deck only has a single copy of the most powerful of the Planeswalkers, but the rest of the deck looks pretty sweet too.
Nykthos, Shrine to Nyx is the real focus of the deck, and the amount of mana this build can generate is absurd. It has the same Burning-Tree Emissary engine as the Standard lists but uses a bunch of Modern-only additions to take Nykthos from an additional few mana to an additional twenty. Cloudstone Curio combines with Elvish Visionary, Eternal Witness, and Burning-Tree Emissary to draw a ton of extra cards, either from your deck or your graveyard. Garruk Wildspeaker untaps Nykthos (while providing for devotion) and, even without Nykthos, can ramp into the other engine the deck plays: Primeval Titan.
Titan's power is well-known by now, and despite the fact that there are no Valakuts to fetch here, getting a Forest and a Nykthos is already a huge boost in mana. You can even use Curio to bounce the Nykthos if you haven't played a land yet, leading to some explosive turns. Arbor Elf, Fertile Ground, and Utopia Sprawl round out the ramp spells, and they too combine very well, with all the Auras going on the same Forest for the Elf to untap.
Once you've generated a million mana, you do have to do something with it, and Genesis Wave (plus Karn!) is that thing. Genesis Wave often chains into more Waves, as Eternal Witnesses can bring back previous Waves, and untapped lands and Auras can fuel the next Wave of threats. The new legend rule helps immensely here, as multiple Garruks in the same turn let you continue to untap Nykthos, making it pretty realistic to Genesis Wave every threat out of your deck.
hurrr's Mono-G Genesis Wave
Modern Magic Online Event
Luis Scott-Vargas plays, writes, and makes videos about Magic. He has played on the Pro Tour for almost a decade, and between that and producing content for ChannelFireball, often has his hands full (of cards).