A Simic Elf tribal deck that can transform to Temur Elf tribal. Let's break it down
Key Card: Metallic Mimic - Metallic Mimic is our key card; we can declare Elf as its creature type and give a +1/+1 counters on each other Elf in our deck that enters the battlefield.
Pump Up Creatures/Planeswalkers: Rishkar, Peema Renegade, Nissa, Voice of Zendikar, Verdurous Gearhulk - Our main +1/+1 counter distributors, pumping up all Elves with Rishkar providing additional mana to use.
Main Threats: Sylvan Advocate, Skyrider Elf, Walking Ballista, Cultivator of Blades - Solid Cards and cheap to cast with the exception of Cultivator however, the mana ramp that Servant of the Conduit provides along with Rishkar might help to cast early. Put the counters on Cultivator then swing for a minimum +3/+3 that goes to all your creatures.
Defence: Narnam Renegade - This creature with deathtouch is our defence against huge or o/p creatures as it will hold them at bay or if we go to offence and opponent does not have many creatures, it will guarantee damage.
Tools for Win:Blossoming Defense, Heroic Intervention, Armorcraft Judge - Blossoming Defence and Heroic Intervention will provide the protection and the time we need to pump our creatures up and swing for the win. Armorcraft Judge will benefit us by drawing cards for each creature we have with a +1/+1 counter on it so in most cases we will draw at least 2 cards.
Removals: Disallow - There's always space for a good removal, utilise against Saheeli Combo or any other combo that can determine the game.
Sideboard: Radiant Flames, Kozilek's Return - Transform the deck to Temur with these cards in case you are playing against aggro decks (probably Mardu Vehicles).
Negate - Replace other spells if opponent plays a control deck.
Heroic Intervention - Add to main deck if opponent uses mass removal
I hope you find this deck fun to play, I have not done much testing but so far it looks promising. I am open to any suggestions for changes as long as it does not affect the tribal theme. This deck is based on cards I own so any changes will be subject to possible trades I can do!!!