Forest

Elvish Vanguard

Whenever another Elf enters, put a +1/+1 counter on Elvish Vanguard.

Wirewood Lodge

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

Stabilizer

Doom Cannon

As Doom Cannon enters, choose a creature type.
{3}, {T}, Sacrifice a creature of the chosen type: Doom Cannon deals 3 damage to any target.

Primal Whisperer

Primal Whisperer gets +2/+2 for each face-down creature on the battlefield.
Morph {3}{G} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)

Alpha Status

Enchant creature
Enchanted creature gets +2/+2 for each other creature on the battlefield that shares a creature type with it.

Timberwatch Elf

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

Seedborn Muse

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

Silklash Spider

Reach
{X}{G}{G}: Silklash Spider deals X damage to each creature with flying.

Upwelling

Players don't lose unspent mana as steps and phases end.

Elvish Guidance

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

Elvish Pathcutter

{2}{G}: Target Elf creature gains forestwalk until end of turn. (It can't be blocked as long as defending player controls a Forest.)

Wirewood Herald

When Wirewood Herald dies, you may search your library for an Elf card, reveal that card, put it into your hand, then shuffle.

Ambush Commander

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.

Wellwisher

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

Steely Resolve

As Steely Resolve enters, choose a creature type.
Creatures of the chosen type have shroud. (They can't be the targets of spells or abilities.)

Heedless One

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

Wirewood Channeler

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