Post Big-Bang, Alishar will already be at its throne.
Note: Beware of Chronos, Platoon Chronos and Master Chronos that Alishar may summon. Also beware of Alishar's seal and darkness skills. It's recommended that most of the spawn is killed before Alishar, or lower levelled party members may die when the treasure boxes pop-up appears.
Once Alishar is killed, a treasure box pop-up will appear with 6 treasure boxes. Randomly choose one and you'll be allowed to choose 1 prize among 3 different prizes.
Remember to pick up the Key Ring dropped by Alishar; then talk to the Purple Balloon to exit the stage.
