Llanowar Elves

Timberwatch Elf

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

Llanowar Druid

{T}, Sacrifice Llanowar Druid: Untap all Forests.

Priest of Titania

{T}: Add {G} for each Elf on the battlefield.

Taunting Elf

All creatures able to block Taunting Elf do so.

Elvish Soultiller

When Elvish Soultiller dies, choose a creature type. Shuffle all creature cards of that type from your graveyard into your library.

Titania's Chosen

Whenever a player casts a green spell, put a +1/+1 counter on Titania's Chosen.

Eladamri, Lord of Leaves

Other Elf creatures have forestwalk. (They can't be blocked as long as defending player controls a Forest.)
Other Elves have shroud. (They can't be the targets of spells or abilities.)

Kaysa

Heedless One

Trample
Heedless One's power and toughness are each equal to the number of Elves on the battlefield.

Seedtime

Cast this spell only during your turn.
Take an extra turn after this one if an opponent cast a blue spell this turn.

Wellwisher

{T}: You gain 1 life for each Elf on the battlefield.

Wood Elves

When Wood Elves enters, search your library for a Forest card, put that card onto the battlefield, then shuffle.

Gaea's Herald

Elvish Champion

Other Elf creatures get +1/+1 and have forestwalk. (They can't be blocked as long as defending player controls a Forest.)

Wirewood Hivemaster

Whenever another nontoken Elf enters, you may create a 1/1 green Insect creature token.

Wirewood Channeler

{T}: Add X mana of any one color, where X is the number of Elves on the battlefield.