Cobra blade

You summon a scimitar with a greenish aura to your hand. As an action you can make a melee attack with it. It does 1D6 slashing dmg. On a hit, the creature also needs to make a constitution saving throw or take 2D4 extra poison dmg. You can keep the blade until you dismiss it.
This spell's damage increases by 1d4 when you reach 5th level (3d4), 11th level (4d4), and 17th level (5d4).