Legacy MonoGreen Elves (Aggro) with NO.
16 Land variant
Sideboard needs metagame optimization - currently 1 card extra, usual suspects in there but other possibilities exist depending on local conditions.
A list of variations on the "base" NO Elves deck:
16 lands instead of 18: inclusion of 4 Sylvan Rangers, which help fish forests out, and provide CA. Serves to improve card quality by thinning deck, and also allows the deck to be relatively land-light, as they help to ensure critical 2nd (and 3rd) land drops are more regularly used - effect only really useful in land-scarce builds such as these. Competes with Elvish Visionary, 4:2 split seems optimal for reducing land count (which also helps increase Elf count!). The use of 6 "cantrip" elves, along with 4 Sylvan Messengers, give good CA to this deck. Cute convenient trick combining either with Wirewood Symbiote as a CA engine.
3x GSZ, missing fourth. Partly due to lack of MD space, partly because GSZ gets shuffled back, and given that 10 cards in the deck provide CA of some sort, should be seeing enough of GSZ over the course of the game. 4th GSZ versus 4th NO is up for debate.
Lack of Gaea's Cradle: Usually a singleton anyway, increases vulnerability to Wasteland, and useless if the only land in opening hand (particularly bad in a land-light build where single land hands are more common). (Also $$$) The only nonbasic is a Dryad Arbor, which is a backup plan for use with GSZ turn 1 in absence of mana dork, and Plan C is to actually use it as a land drop (Plan D is to use it as the first land drop!).
Terastodon in sideboard, Wirewood Symbiote (as a 1-of) in main. Metagame choice. GSZ allows the inclusion of a singleton Wirewood Symbiote, which has many uses whilst taking up minimal deck space. Optional. Also, Viridian Zealot x1 already main, so there are answers to pesky artifacts and enchantments maindeck game 1, tutorable with GSZ.
In general, this deck, with 37 elves, makes Sylvan Messenger that much more effective, particularly with the deck thinning effect of Sylvan Ranger. GSZ toolbox allows this deck to pack more singleton answers and utility creatures like Quirion Ranger and Wirewood Symbiote and Dryad Arbor, and have more options - NO-Prog finisher, GSZ-Ezuri finisher, multiple lords+horde finisher, etc.
Suggested sideboard is a broad all-comers (jack-of-all-trades, master-of-none) suite.