DEVOUR YOUR OPPONENTS!
I wanted to make a modern deck that would work around the devour mechanic and be optimized to really punch your opponent in the gut. So this deck ended up happening. The main star, Mycoloth, has devour 2 and will shit out saprolings each turn equal to the number of +1/+1 counters on him. This gives you quite a number of creatures to work with. Ideally, you'll be turning out dozens or even hundreds of saprolings each turn. Overall I'm pretty satisfied with the outcome, but if anybody has any suggestions (please just try to keep it modern though), I'd love to hear them!
So there's obviously a lot going on in this deck. The first thing you're going to want to do is stay alive long enough to get your heavy sluggers out. That's where Bloodhall Ooze shines. I guarantee that it'll grow faster than your opponent's creatures can keep up (you're likely getting two +1/+1 counters on it every turn, and that's BEFORE Corpsejack Menace or Doubling Season come in). Cards like Khalni Garden and Utopia Mycon will give you a few blockers early-game to help with that as well. Speaking of Utopia Mycon, as well as producing saprolings, it also gives you a slight boost in your manaramping by sacrificing saprolings. Sprouting Thrinax is also good for defending you early-game and then giving you more fodder to devour or blockers to keep your health high. Then comes Krenko, Mob Boss. He'll likely be a bit slow to start off, but he'll give you exponential token production, so that definitely won't hurt. He's also the reason I threw in Mirror Entity and the "vivid" lands, so that all of your saprolings can now count as goblins, letting your production really take off. So what do you do with all of these creatures now? Well you can either go for a head-on assault, obviously outnumbering your opponent's creatures, or you can feed them to Mycoloth. What makes Mycoloth so ridiculous is his devour 2 ability. If you devour just four saprolings, he'll turn into a 12/12 creature, and if that wasn't scary enough on its own, you're also getting eight saprolings to attack/block with EVERY TURN. Now think about what that turns into if you have either a Doubling Season, Parallel Lives, or Corpsejack Menace on the field before it sets out on its feast. If you happen to have all three out at a time, devouring four saprolings/creatures will now get you a 36/36 creature, and while your opponent is busy wetting themselves at that sight, you can shit out 128 saprolings every turn. Now let's say you devoured five instead of four. You're now looking at a 44/44 creature and 160 saprolings each turn. Now don't get me started on if you have an extra doubling season or whatnot out at that time. Of course you could always swing to kill with all your creatures, but if you want to get really sadistic, why not take those 160 saprolings (which you'll get back next turn anyway) and give it to ANOTHER Mycoloth? With all three of the doubling buffs out, you're looking at a 1284/1284 creature that will pump out 5,120 saprolings each turn (Feel free to laugh at your buddy's puny Eldrazi creature). This will be the point where your friends will likely give up Magic for good. You don't have to be great at math to see that this really adds up. Just for the sake of good humor, I also threw an Akroma's Memorial in there, so those thousands of 1/1 saprolings can also have flying, first strike, vigilance, trample, haste, and protection from black and red. That's really all you need for the deck, but the rest of the cards help quite a bit too. Blade of the Bloodchief, Death's Presence, Soul's Might, and Llanowar Reborn will help give your Mycoloth a little boost if he didn't devour quite enough creatures when he came out, so don't worry about him going hungry anytime soon. Blood Artist can bring the pain directly to the opponents when you devour, so it'll definitely help get through pesky tactics (like indestructible Palace Guards for instance), with the added benefit of keeping you healthy. Leyline of Vitality will also heal you when your creatures come out, so if you have both of them out, you're gaining life when your creatures come out as well as when they become a Mycoloth meal. Fecundity and Grave Pact are also pretty great at giving you the upper-hand because for each creature you devour, you not only get to draw a card if you'd like, but your opponents have to match your meal and sacrifice their own creatures. So all in all, you've got a deck here that's pretty relentless and gives you plenty of options to work with, so as long as nobody throws out a Wrath of God, you can feed your ever-growing hunger until there's nothing left of the opponent.