Alfi's Liquid Blade

You evoke a blade of water in your free hand. The blade is similar in size and shape to a scimitar, with the light and finesse properties, and it lasts for the duration. If you let go of the blade, it vaporizes into the flask, but you can evoke the blade again as a bonus action.

You can use your action to make a melee spell attack with the liquid blade. On a hit, the target takes 2d8 radiant damage + the caster's spell attack modifier.

Requiring no additional action after the blade has been evoked, you can freeze the liquid blade into solid ice, changing the damage to 2d10 cold damage + the caster's spell attack modifier on a hit. When in solid form, the blade shatters and ends the spell on a missed attack. 

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage dice increase by 1d8/1d10 per 2 levels above 2nd.