Venombrand Weapon

You wreathe a weapon you are holding in dripping venom.

Until the spell ends, when you hit with the weapon, the target takes an extra 1d6 poison damage on hit.

Toxic Wound

The target has disadvantage on its next attack roll before the end of its next turn.

Elemental Resonance. When you cast a spell of the same element while this spell is active, its effects intensify. The first time you do so before the spell ends, increase the extra damage by 1d6 and enhance the rider effect (described in each spell). This benefit can occur only once per casting.

Elemental Resonance (Poison)
Extra damage becomes 2d6
Target is poisoned until the end of its next turn
If already poisoned, it takes an additional 1d6 poison damage