There are a number of ways to build a ramp deck in Modern. Some focus on Scapeshift, some don’t. This deck ties together the ability to ramp out lands into Valakut, the Molten Pinnacle with a back-up planeswalker combo.
At the forefront is Primeval Titan. Getting a Titan into play lets you search up a pair of Valakuts. With enough lands in play, the first attack will find 2 Mountains and result in 12 damage spread out evenly among up to 4 targets (or just 12 to your opponent).
There happens to be a great way to accelerate this process. Through the Breach can be cast a turn sooner than Primeval Titan, but does so much more. By giving your Titan haste, you can fetch 2 Valakuts, attack, fetch 2 Mountains to deal 12, and threaten 6 more damage from your trampler. Suspending a turn-1 Search for Tomorrow into any 2-mana ramp spell makes this a turn-3 play!
Scapeshift is the top-end of this deck, although it only costs 4 mana and isn’t entirely necessary. Primeval Titan will get the job done at what should be a lower cost, but Scapeshift has benefits. It will end the game immediately; is stronger against removal, Mana Leaks, and Remands; and can end the game from incredibly high opposing life totals if you’re able to put enough lands into play.
Many versions of this deck run Oath of Nissa as an additional means to find lands or Tribe Elders and, more importantly, Primeval Titans. It’s a solid card, but doesn’t find any of the other ramp spells and finding lands isn’t always useful. This version cuts them for more interaction and Scapeshifts.
Nahiri, the Harbinger is much easier to cast with Oaths in the deck, but you’re playing a ramp strategy that can find you white mana in a pinch. You’re really not thrilled to play basic Plains to fetch with your Tribe Elders and Searches, but Nahiri is that powerful. This is your main answer to cards like Blood Moon, especially in game 1. You can kill creatures, and you can tick your Nahiri up to ultimate. It can be awfully tempting to play Emrakul, the Aeons Torn in any deck with Nahiri, but this is the lone strategy that actually doesn’t need it, since Primeval Titan will end the game such a huge percentage of the time that you fetch one with Nahiri thanks to the 18-damage combo with Through the Breach. In this case, Primeval will actually return to your hand at the end of turn in case you needed to get even more hits!
Nahiri’s power is widespread throughout Modern, enabling entire combo decks while supplementing other decks. Being able to rummage through the cards you don’t need is so important to these strategies, and she lets you do it each turn while advancing your game plan and for no additional mana investment. Nahiri, the Harbinger is doing work to become the defining planeswalker in all of Modern, and this deck is another example of why!