Bile stream

You ingest a piece of rotten flesh to magically force yourself to vomit a toxic cone of acid in a 15 feet cone. The surface remains coved in the vile acid for the spells duration. Should concentration fail the acid remains an additional 1d4 rounds, dealing half the original spell slot damage.

DEX save vs half.

Damage = 2d4 Acid.

At the start of a failed creatures turn they take additional acid damage equal to half the casted spell slot damage, they must use an action to remove the acid. (Stepping out of the stream does not remove the acid) A creature entering the area for the first time must make a DEX save vs half the original spell slot damage.

Higher spell slot usage: 2nd level and higher the damage scales an additional 2d4. 

Starting at level 10 you have mastered control of the stream. You may now instead choose to spray the stream in a 30 feet long 5 feet wide straight line.