Pit Scorpion
{2}{B}
Creature -- Scorpion
1/1
Whenever ~this~ deals damage to a player, that player gets a poison counter. (A player with ten or more poison counters loses the game.)
Sabertooth Cobra
{2}{G}
Creature -- Snake
2/2
Whenever ~this~ deals damage to a player, that player gets a poison counter. The player gets another poison counter at the beginning of their next upkeep unless they pay {2} before that step. (A player with ten or more poison counters loses the game.)
Serpent Generator
{6}
Artifact
{4}, {T}: Create a 1/1 colorless Snake artifact creature token. It has "Whenever ~this~ deals damage to a player, that player gets a poison counter." (A player with ten or more poison counters loses the game.)