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.

Crypt Cobra

Whenever Crypt Cobra attacks and isn't blocked, defending player gets a poison counter. (A player with ten or more poison counters loses the game.)

Orochi Hatchery

Orochi Hatchery enters the battlefield with X charge counters on it.
{5}, {T}: Create a 1/1 green Snake creature token for each charge counter on Orochi Hatchery.

Serpent Assassin

When Serpent Assassin enters the battlefield, you may destroy target nonblack creature.

Wall of Vipers

Defender (This creature can't attack.)
{3}: Destroy Wall of Vipers and target creature it's blocking. Any player may activate this ability.

Coiled Tinviper

Butch DeLoria, Tunnel Snake

Menace (This creature can't be blocked except by two or more creatures.)
Tunnel Snakes Rule! — Whenever Butch DeLoria, Tunnel Snake attacks, it gets +1/+1 until end of turn for each other Rogue and/or Snake you control.
{1}{B}: Put a menace counter on another target creature. It becomes a Rogue in addition to its other types.

Hagra Constrictor

Hagra Constrictor enters the battlefield with two +1/+1 counters on it.
Each creature you control with a +1/+1 counter on it has menace. (A creature with menace can't be blocked except by two or more creatures.)

Gravebreaker Lamia

Lifelink
When Gravebreaker Lamia enters the battlefield, search your library for a card, put it into your graveyard, then shuffle.
Spells you cast from your graveyard cost {1} less to cast.

Vector Asp

{B}: Vector Asp gains infect until end of turn. (It deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

Serpent Warrior

When Serpent Warrior enters the battlefield, you lose 3 life.

Zombie Boa

{1}{B}: Choose a color. Whenever Zombie Boa becomes blocked by a creature of that color this turn, destroy that creature. Activate only as a sorcery.

Zodiac Snake

Swampwalk (This creature can't be blocked as long as defending player controls a Swamp.)

Yuan-Ti Fang-Blade

Deathtouch
Whenever Yuan-Ti Fang-Blade deals combat damage to a player, venture into the dungeon. (Enter the first room or advance to the next room.)

Rotting Fensnake

Pharika's Chosen

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

Skeletal Snake

Zagoth Mamba

Whenever this creature mutates, target creature an opponent controls gets -2/-2 until end of turn.

Ukud Cobra

Stonecoil Serpent

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

Erebos's Emissary

Bestow {5}{B} (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature.)
Discard a creature card: Erebos's Emissary gets +2/+2 until end of turn. If Erebos's Emissary is an Aura, enchanted creature gets +2/+2 until end of turn instead.
Enchanted creature gets +3/+3.

Python

Snake Basket

{X}, Sacrifice Snake Basket: Create X 1/1 green Snake creature tokens. Activate only as a sorcery.

Ophiomancer

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

Soulcoil Viper

{B}, {T}, Sacrifice Soulcoil Viper: Return target creature card from your graveyard to the battlefield with a finality counter on it. Activate only as a sorcery. (If a creature with a finality counter on it would die, exile it instead.)

Sivriss, Nightmare Speaker

{T}, Sacrifice another creature or an artifact: For each opponent, you mill a card, then return that card from your graveyard to your hand unless that player pays 3 life. (To mill a card, put the top card of your library into your graveyard.)
Choose a Background (You can have a Background as a second commander.)

Thieving Amalgam

At the beginning of each opponent's upkeep, you manifest the top card of that player's library. (Put it onto the battlefield face down as a 2/2 creature. Turn it face up any time for its mana cost if it's a creature card.)
Whenever a creature you control but don't own dies, its owner loses 2 life and you gain 2 life.