You've learned how to combine your affinity to lightning with your skill of learning the combat capabilities of your enemies.
You mark a creature that you can see within range with a electric pulse and affect one of its capabilities. Until the spell ends, you deal an extra 1d6 lightning damage to the target whenever you hit it with an attack. Also, choose one ability when you cast the spell. The target has disadvantage on ability checks made with the chosen ability.
If the target drops to 0 hit points before this spell ends, you can use a bonus action on a subsequent turn of yours to curse a new creature. A remove curse cast on the target ends this spell early.
At Higher Levels: When you cast this spell using a spell slot of 3rd or 4th level, you can maintain your concentration on the spell for up to 8 hours. When you use a spell slot of 5th level or higher, you can maintain your concentration on the spell for up to 24 hours.