One of your arms briefly transforms into a venomous serpent which strikes out at an enemy. Make a melee spell attack against a creature in range. On a hit the creature takes 1d6 poison damage and must succeed on a Constitution saving throw or be poisoned until the end of its next turn. 

The damage of this spell increases by 1d6 when you reach 5th level (2d6), 11th level (3d6), and 17th level (4d6).