Timberwatch Elf

{T}: Target creature gets +X/+X until end of turn, where X is the number of Elves on the battlefield.

Arbor Elf

Llanowar Elves

Farhaven Elf

When Farhaven Elf enters, you may search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Wirewood Elf

Galadriel, Light of Valinor

Alliance — Whenever another creature you control enters, choose one that hasn't been chosen this turn —
• Add {G}{G}{G}.
• Put a +1/+1 counter on each creature you control.
• Scry 2, then draw a card.

Imaryll, Elfhame Elite

Whenever Imaryll, Elfhame Elite attacks, it gets +X/+X until end of turn, where X is the number of other Elves you control.
You may have Imaryll assign its combat damage as though it weren't blocked.