Seed the Land

Whenever a land enters, its controller creates a 1/1 green Snake creature token.

Forest

Ophiomancer

At the beginning of each upkeep, if you control no Snakes, create a 1/1 black Snake creature token with deathtouch.

Pharika's Chosen

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)

Ukud Cobra

Blight Mamba

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
{1}{G}: Regenerate Blight Mamba.

Stonecoil Serpent

Reach, trample, protection from multicolored
Stonecoil Serpent enters with X +1/+1 counters on it.

Hooded Blightfang

Deathtouch
Whenever a creature you control with deathtouch attacks, each opponent loses 1 life and you gain 1 life.
Whenever a creature you control with deathtouch deals damage to a planeswalker, destroy that planeswalker.

Sosuke's Summons

Create two 1/1 green Snake creature tokens.
Whenever a nontoken Snake you control enters, you may return Sosuke's Summons from your graveyard to your hand.

Swamp

Animal Sanctuary

{T}: Add {C}.
{2}, {T}: Put a +1/+1 counter on target Bird, Cat, Dog, Goat, Ox, or Snake.

Snake of the Golden Grove

Tribute 3 (As this creature enters, an opponent of your choice may put three +1/+1 counters on it.)
When Snake of the Golden Grove enters, if tribute wasn't paid, you gain 4 life.

Pharika, God of Affliction

Indestructible
As long as your devotion to black and green is less than seven, Pharika isn't a creature.
{B}{G}: Exile target creature card from a graveyard. Its owner creates a 1/1 black and green Snake enchantment creature token with deathtouch.

Golgari Rot Farm

Golgari Rot Farm enters tapped.
When Golgari Rot Farm enters, return a land you control to its owner's hand.
{T}: Add {B}{G}.