Confession time: I think Theros block is super cool, but I feel the majority of its coolness comes from its flavor implementation, rather than from its mechanics. Still, it does have a mechanic called MONSTROSITY so it would be criminal not to build a deck around it.
Specifically I’m interested in Nemesis of Mortals. Here’s a deck featuring that super-scary snake:
4 Nemesis of Mortals
4 Dawntreader Elk
4 Viridian Emissary
2 Uktabi Drake
4 Elvish Visionary
4 Culling Dais
4 Wildwood Rebirth
4 Beast Within
2 Mighty Emergence
18 Other Spells
Ok, as you can imagine this deck centers around putting your own creatures into the graveyard to make Nemesis of Mortals easier to cast. This deck also features Splinterfright. This elemental will be your win condition in a lot of games, while your opponents worry about your 10/10 superviper they’ll likely ignore your 3/3 (or 5/5, or 9/9) trampler. Splinterfright also has the added bonus of making himself bigger by milling you for 2 every turn.
THE OTHER GUYS
The other creatures in this deck (and this is a creature-heavy deck) are largely there to be corpses. I chose them for their ability to sacrifice themselves or for the bonuses they give you when you feed them to a Culling Dais. Of special note are Dawntreader Elk and Viridian Emissary who pull double-duty of being tasty bones for splinterfright to wear AND building your mana up so you can BOOM-SHAKA-MONSTRIFY even faster.
Although they’re in the minority, this deck features a few non-creature cards to help things along. The aforementioned Culling Dais draws you cards and gives you a sacrifice outlet, Wildwood Rebirth allows you to re-use your dead creatures, mighty emergence adds insult to injury making your bruisers even bigger. Note though that putting counters on Nemesis of Mortals doesn’t monstrify it, Monstrosity is its own ability. Bonehoard acts as a secondary Splinterfright, with the additional bonus of, say, turning an elvish visionary into a massive threat.
If you wanted to add different cards to this deck you might consider swapping out Nemesis of Mortals for Ghoul Tree, thus getting all your power at once (there are pros and cons to both). Obviously throwing in some black would allow more graveyard synergy as well as more reliable ways to reanimate your creatures. Red could give you access to cards like Hissing Iguanar, adding bonus damage whenever you crunch a creature. Lastly, blue cards like Tome Scour would allow you to dump creatures into your graveyard even faster, but honestly I think the deck does a good job of that already.
There is a lot of room for customization with this deck, if you guys get a chance to put this together let me know how it plays and what changes you’d make.