Llanowar Elves

Thud

As an additional cost to cast this spell, sacrifice a creature.
Thud deals damage equal to the sacrificed creature's power to any target.

Forest

Sylvan Caryatid

Defender, hexproof
{T}: Add one mana of any color.

Steel Leaf Champion

Steel Leaf Champion can't be blocked by creatures with power 2 or less.

Utopia Sprawl

Enchant Forest
As Utopia Sprawl enters, choose a color.
Whenever enchanted Forest is tapped for mana, its controller adds an additional one mana of the chosen color.

Fauna Shaman

{G}, {T}, Discard a creature card: Search your library for a creature card, reveal it, put it into your hand, then shuffle.

Burning-Tree Emissary

When Burning-Tree Emissary enters, add {R}{G}.

Mountain

Ghalta, Primal Hunger

This spell costs {X} less to cast, where X is the total power of creatures you control.
Trample