A bartender's utility scroll that changes the chemical composition of water in a container, weaponized into acid.
Rather than stock the bars with many different types of alcohol, the Showrunners issued NPC bartenders a few scrolls able to alter the chemical composition of water within a container. It was never intended as combat magic.
Team Retribution's NPC spies discovered the loophole: treat the enemy's empty middle trench as the "container." They filled it with a Temporary Water Source Scroll and converted the water into acid, creating the Acid Trench. Carl calls it a horrifying spell, and Baroness Victory tells him the rules on what counts as "offensive" magic may need revisiting because the chemical alteration spell is a little too powerful.
A civilian utility scroll whose loophole produced the battle's worst massacre.