Elves is one of my favorite decks. I play combo Elves.
Ruric Thar, the Unbowed is in the sideboard for Storm, High Tide, or Burn. The meta in my area is plagued with Storm and Burn. High Tide will occasionally make an appearance. Cavern of Souls on Warrior allows you to cast Ruric Thar and several Elves without worry.
Previous Card Choices
Leovold, Emissary of Trest was main. I really dislike playing the card because of having to maintain board state. It helps out against more match ups than I am willing to admit. My local meta is pretty similar to this, so Leovold does well against Miracles, and with Mindbreak Trap in the side, it helps out in a lot of other match ups as well.
Mindbreak Trap was in the sideboard against combo. When Storm and RB Reanimator ran free and wild, it was nice to have an answer.
Nissa, Vital Force was in the sideboard for mostly blue decks. She helps with the beat-down route and is difficult to remove.
I find that if I don’t have Cavern of Souls in hand against a Chalice on 1, Wolf-Skull Shaman is something I can easily cast or Green Sun’s Zenith for without much trouble. It also helps to build up some board state. It has helped a little against Miracles. If you hit Elves, it’s great, but I run ~20 other elves, which means each flip is a little more than a 1 in 3 chance.
I found the card dies to easily in the current meta. BUG and 4-color Control remove it quickly. In match-ups where it sticks, it’s usually already in Elves’ favor. I like it against Stompy decks if I can get it to stick.
Gilded Drake is one of my favorite sideboard cards. It works well against Renimator, Show n Tell, Eldrazi, or other Stompy decks. Being a 3/3, it survives and trades with Elesh Norn, Grand Cenobite, letting you cast elves again.
The meta is no longer Renimator or Show n Tell heavy, so I removed this from the sideboard.