Wirewood Pride

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

Elvish Soultiller

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

Forests you control are 1/1 green Elf creatures that are still lands.
{1}{G}, Sacrifice an Elf: Target creature gets +3/+3 until end of turn.

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

Creatures of the creature type of your choice get +X/+X until end of turn.

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

{T}: Add {C}.
{G}, {T}: Untap target Elf.

Untap all permanents you control during each other player's untap step.

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

Enchant land
Whenever enchanted land is tapped for mana, its controller adds an additional {G} for each Elf on the battlefield.

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

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