Main Deck
This deck is primarily about the Elvish Archdruid + Umbral Mantle combo that permits an arbitrary amount of mana and arbitrary power/toughness for all tappable elves. There is also lots of ramp and a hint of Elf Ball.
Arbor Elf, Llanowar Elves: Mana dorks; the bread and butter of the deck
Heritage Druid
: Gives elves "mana haste"
Commune with Nature: Elvish Archdruid finder
Summoner's Pact: Elvish Archdruid tutor
Steelshaper's Gift: Umbral Mantle tutor
Regal Force: Card draw, duh
Elvish Archdruid: Big mana, part of combo with Umbral Mantle
Umbral Mantle: Allows Elvish Archdruid to go infinite, allows use of the mana to pump all tappable elves
Joraga Treespeaker: Mana dork, makes all elves tappable
Staff of Domination: Alternative to Umbral Mantle. Harder to play, but guarantees a win most of the time if it resolves. Bonus: once it's out you can be like "aight now I'll just draw half my deck now, gain 1000 untap all my creatures, tap all your creatures, play this Umbral Mantle, give all my creatures +1000/+1000 and attack you"
Swiftfoot Boots: Protects Elvish Archdruid and allows him to combo off on his first turn of play
Sideboard
This is an aggro sideboard. Use it when you don't think you can pull off the infinite mana combo.
Craterhoof Behemoth: No one runs fog, right?
Joraga Warcaller: Mana sink, huge anthem
There's also this card against swarm decks:
Rancor: To combat pesky chump blockers
Finally, against Ethersworn Canonist and the like, we have:
Viridian Zealot: Artifact/enchantment hate on a stick
Krosan Grip: Uncounterable artifact/enchantment hate
Weaknesses
This deck sucks against mass burn. In combo mode, it also sucks against control, but the sideboard is there to give it a but more of an aggro edge where it doesn't really matter what you play so long as you play lots of elves. I think, however, that this deck's primary weakness is players who ask you to carry out each step of your infinite mana combo.
Maybeboard
Nettle Sentinel: Strong early beater, combos with
Heritage Druid
for fast mana
Lightning Greaves: Alternative to Swiftfoot Boots that additionally gives elves "mana haste" like
Heritage Druid
. Unfortunately, gives shroud instead of hexproof which makes Elvish Archdruid vulnerable to instant removal if I have to equip him with Umbral Mantle