Dissidia Thunder Barret is a ground magic Bravery attack for Squall, learned at level 6. It requires 30 CP to equip (15 when mastered), 120 AP to master, and has Melee Low priority. Squall fires a string of lightning that drags the opponent closer which can also destroy stage elements.
Dissidia012 Thunder Barret is a Bravery attack for Squall, learned at 9 and requiring 90 AP to master. It is otherwise identical to its previous incarnation.
Thunder is the sound caused by lightning. Depending on the distance and nature of the lightning, thunder can range from a sharp, loud crack to a long, low rumble (brontide).