This is just a little deck that began construction today when giving mono-green modern a shot, just using cards I already owned (and more often than not ones just plain pulled)
Changes may be slight, as from creation onwards, it's a Budget deck, because I know buying Modern cards can be fairly expensive.
Explanation time:
Dungrove Elder It's rather obvious, but it's a great and cheap card for a mono-green deck just for getting a high power/toughness later in the game and through basic land gaining.
Elvish Archdruid Again, obvious mana-ramping and bumping my own lowly elves higher.
Elvish Champion Making elves stronger again, and the Forestwalk isn't a bad option either.
Gigantiform Making any 1/1 a total 8/8 trampling beast. And in this deck by the time I can cast it, it's been really likely I can kick it for a second 8/8.
Gladecover Scout a one drop with hex proof that can be boosted through Elvishes and Gigantiform just make it better.
Viridian Betrayers a 3/1 to begin with, and by the time this is out I'm likely to have a booster creature out to increase the low toughness, and it doesn't neccessarily have infect right away. Possibility this will be removed in place of other spells.
Viridian Corrupters the Infect isn't a bad option of other win mechanics, and also makes sac-blocking better as I an perminantly leave a powerful creature weakened. The enter trigger is also just a little non-needed bonus.
Viridian Emissary get another forest out. Need I say more.
Skarrg Goliath a 9/9 for 8 with Trample, or for 7 buff something else with +9/+9. Put this on top of a Gigantiform'd creature, and even with the Elvish buffs, it's going to be swinging for 17/17 with trample, on top of anything else the basic creature had.
Mwonvuli Beast Tracker I seriously search for at least half of my creatures in my deck. There is nothing wrong with this card. Pull my 2 mana costing 3/2 trampler, or Slime when I wanna get rid of a land, or... you get the idea. I can get a lot of my creatures with this.
Green Sun's Zenith ... seriously? This does not need explaining. I'm 99% of the time spending 4 mana and getting either Mwonvuli, Archdruid, etc. And I can do it again if I draw into it! Wish it wasn't banned in actual modern though, I don't use the combo that got it banned.
Elvish Archer a base 1/2 for 1, that blocking a flying becomes 4/2. That sounds good to me.
Acidic Slime do i need to explain this really? It's rather obvious I'm gonna destroy a land with it, and it makes a good blocker too with it's deathtouch.
Creeping Renaissance in a creature heavy deck, this works well I've found, just because it can pull back the mana-elves for me to just increase my squads.