Been testing a singleton
Fierce Empath in the deck, been outrageously successful. Sometimes it feels like I'm running 10 emrakuls in the deck.
The beauty of it is in the simplicity of the fact that your opponent doesn't know how much mana you can produce unless they're quite good at playing elves themselves and have a decent estimation of your hand.
Several things about the card: when you combo you basically win outright--it's nearly impossible not to produce 18-19 mana when comboing off and any GSZ or Pact results in an immediate win. Elves isn't a deck that fizzles -that- often, but it happens. This basically removes that chance without interfering with the deck's natural flow.
More importantly however, games are faster. This goes back to tournament reports I've read (and felt first hand) of Solidarity, where..while the win is inevitable, sometimes actually accomplishing that win is tedious and long--anyone else been in those games where you're sitting on a mountain of mana and emrakul is the third card from the bottom? So instead of trying to find one card, I'm trying to find one of any ten cards that win me the game during the combo. Those long games are mentally draining and exhausting, keeping track of your mana, drawing, which untappers you've used, your pile of tapped elves, how many pacts you've used for the upkeep trigger.. it's a lot to remember and think about when you have to do it every game.
To elaborate on my first point-- if you generate four mana knowing full-well you can generate 15 at any given moment, and you open with a green sun for 3, it's easy to let that slide since they're focusing on dealing with glimpse or tutors for regal force.