Toxic Strike

Evocation Cantrip
Casting Time: 1 action
Range: Self
Components: SM* (a melee weapon)
Duration: 1 round

Target. One creature within the reach of your weapon.
Attack Roll. Melee weapon attack with the weapon used to cast the spell.
Hit. The weapon attack's normal damage + 1d6 poison damage. If the target is Poisoned, or becomes Poisoned as a result of this attack, it deals an additional 1d12 poison damage instead. A creature hit with this attack has Disadvantage on saving throws against poisons until the start of your next turn.
Cantrip Progression. This spell's damage increases when you reach higher levels. At 5th level, the melee attack deals an extra 1d6 poison damage or 1d12 poison damage to the target. The damage roll increases by 1d6 or 1d12 at 11th level, 17th level, 23rd level, and 28th level.

Source: Homebrew