This is a really nice example of an archetype I like to call "soft combo." A hard combo deck will try to win in only one or two explosive turns with an alternate win-con, an infinite combo, or overwhelming damage, but a soft combo deck is fine with spreading the hurt out over time, as long as it still gets there. It's not really a midrange deck - it's midrange-y, playing cards for value and trying to stay on curve - but it wins by establishing an engine and feeding that engine, not just out-valuing the opponent and eventually winning with efficient creatures (though it can totally take a game or two that way, too). It lacks the explosiveness of hard combo, but it's much more consistent and significantly harder to disrupt.

CREATURES

Any combo engine in MTG consists of value and payoff, and in this deck the value looks like Dryad of the Ilysian Grove and the payoff looks like Dread Presence. As you play lands - and with the Dryad, you're gonna be playing a ton of them, and they're all gonna be Swamps - you can drain things for 2 (including your opponent) or draw cards for a little life, which before long should overwhelm your opponent, drowning them in damage and card advantage. The Gitrog Monster and Multani, Yavimaya's Avatar are the closest things this list has to midrange win conditions, but in this deck that more or less just means that they provide both value and payoff. Multani's payoff is just being a really big creature, of course, but it's still a welcome addition to the deck, especially given that its ability to come back from the graveyard in exchange for bouncing lands is just upside for more upside here. World Shaper is a bit smaller itself, but it still provides value every time it attacks (this deck really loves having a yard well-stocked with lands), and when it dies with a Dread Presence out, that can just be game.

Courser of Kruphix is a really nice value engine here (or in just about any green deck that cares about lands, but you already knew that), and it tends to synergize really nicely with a Dread Presence and Dryad of the Ilysian Grove already out. Three Ramunap Excavator really kick the engine into high gear - the ability to play lands from the yard is just so good in this deck - and it's your choice whether to run it or Crucible of Worlds, though I like the body on the Excavator. The one-drops are all-stars, too: Deathrite Shaman is only not banned in Pioneer because the absence of fetch lands make its uses more narrow, but it's ridiculously strong here, and Elvish Reclaimer is frequently a 3/4 for 1 that provides all kinds of repeatable value and a place to spend the extra mana that a deck like this tends to make. Plus, if you think about it, both it and Deathrite are just one-drop mana elves with extra steps, and that makes me happy.

NONLANDS

Crop Sigil can hit the battlefield turn 1 and start printing out value, and if you can trigger Delirium, which isn't too hard in this deck, it can pull just what you need back into your hand later in the game. Drown in Filth is value and extremely strong two-mana creature removal, Fork in the Road is a great tutor that gives you a land in the hand and one in the yard, and Grisly Salvage rips through your deck for your best creatures and lands. Just be careful not to deck yourself out!

MANA BASE

The land base in this one is pretty simple. Four each of Overgrown Tomb (as much for the Swamp Forest type line as the fast mana), Woodland Cemetery (because everything here should be a Swamp or a Forest), Fabled Passage (amazing for obvious reasons in a deck that interacts with lands in the yard), your basics, two of Field of Ruin (which is incredibly useful in this list), and a single copy of Urborg, Tomb of Yawgmoth (just another way to turn everything into a Swamp for Dread Presence). Easy, breezy, beautiful, The Gitrog Monster.

SIDEBOARD

The sideboard is divided between more big creatures - Polukranos, Unchained because it's really efficient and can come out of your graveyard and Prowling Serpopard because this deck has some trouble with counter magic - and more removal. Fatal Push is just a great spell overall, especially in a list with lands leaving the battlefield regularly, Broken Bond removes artifacts and plunks down another land for you, Golgari Charm is super versatile and can even protect your creatures in a pinch, and Casualties of War is an excellent mass removal spell that can be brought in to take out pretty much anything thatt can be dealt with at sorcery speed. Assassin's Trophy is just a great card for 2 mana, but you already know about all that.