Acidic Scorcher

A magic, green-and-red flame sprouts from your weapon. Make an attack roll. On a hit, have a single target roll a Constitution saving throw: on a failure, the target takes 2d8 poison damage and 2d8 fire damage and is poisoned, or half as much damage and no poison affect on a successful one. Your weapon is also  magical for the purpose of overcoming resistance and immunity.

When casting this spell using a spell slot higher than 4th, increase both the poison damage and fire damage by 1d8.