Arnic's Misspell Magic

You interrupt the casting of another spell that is in the process of being cast by another creature, altering its properties. If the creature is casting a spell of 3rd level or lower, you alter the spell by adding, substituting, deleting, or moving one character in the spell's name, thus misspelling it. If it is casting a spell of 4th level or higher, make an ability check using your spellcasting ability. The DC equals 8 + the spell's level. On a success, you alter the spell in the same way as described earlier. When a casted spell is misspelled, its effects become changed (DM's discretion), and those effects reflect its new name.

Arnic pointed his wand at the wizard, who seemed to be preparing a spell. A flash in the moment he swore he casted mage armor, Arnic's rival found himself covered in head to toe in paper. 

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, you can alter one additional character in the misspelled spell's name for every slot level above 3rd.