it's really similar to my list; you should add some corpsejack menace it doubles scavenge counters and make a later experiment one a real threat, every opponent I played against at first ignores it then he says: it does... WHAT?
also yeva, nature's herald : playing almost all of your creatures at instant speed it's gorgeous; an instant wolfir silverheart it's a real deal; she makes blocking difficult and attacking really hard for the opponent
4x Arbor Elf
2x Deadbridge Goliath
4x Dreg Mangler
4x Experiment One
3x Gyre Sage
4x Strangleroot Geist
3x Varolz, the Scar-Striped
3x Wolfir Silverheart
2x Golgari Guildgate
4x Overgrown Tomb
2x Swamp
4x Woodland Cemetery
3x Abrupt Decay
3x Putrefy
3x Deathrite Shaman
3x Duress
2x Golgari Charm
2x Pithing Needle
2x Ranger's Guile
3x Vampire Nighthawk
Garruk, Primal Hunter seemed like a strong add.
Other ideas that I just offer for consideration as possible singleton adds:
Craterhoof Behemoth
Yeva, Nature's Herald
Korozda Gorgon
Deadbridge Chant
Skarrg Goliath
Nothing seems bad to me, but maybe go to 3 Strangleroots and/or Rancor.
RNA Standard: Grixis Midrange, Jund Deathwhirler, Sultai Vannifar
GRN Standard: Red Midrange, Mono-Blue Tempo, Wr Aggro, Gruul Experimental Dinosaurs, Sultai Midrange, Jeskai Midrange
Modern: Bant Spirits
Forcing a single archetype in all formats: too many colors, bad mana.
also yeva, nature's herald : playing almost all of your creatures at instant speed it's gorgeous; an instant wolfir silverheart it's a real deal; she makes blocking difficult and attacking really hard for the opponent