Joraga Warcaller

Multikicker {1}{G} (You may pay an additional {1}{G} any number of times as you cast this spell.)
Joraga Warcaller enters with a +1/+1 counter on it for each time it was kicked.
Other Elf creatures you control get +1/+1 for each +1/+1 counter on Joraga Warcaller.

Llanowar Elves

Priest of Titania

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

Immaculate Magistrate

{T}: Put a +1/+1 counter on target creature for each Elf you control.

Forest

Fyndhorn Elves

Beast Whisperer

Whenever you cast a creature spell, draw a card.

Realmwalker

Changeling (This card is every creature type.)
As Realmwalker enters, choose a creature type.
You may look at the top card of your library any time.
You may cast creature spells of the chosen type from the top of your library.

Wellwisher

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

Elvish Archdruid

Other Elf creatures you control get +1/+1.
{T}: Add {G} for each Elf you control.

Imperious Perfect

Other Elves you control get +1/+1.
{G}, {T}: Create a 1/1 green Elf Warrior creature token.

Gaea's Cradle

{T}: Add {G} for each creature you control.

Heedless One

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