In this mission, you are transported back to Surge of Fortunas. All you need to do is to ride the elevator and get the Blue Orb Fragment found at the top. But you have to watch out, because this time, enemies are now in their DT form. To make things worse, when 6 Hell Prides are on the elevator with you, the elevator cannot sustain the weight and will fall. So you need to make sure you eliminate your current enemies before another wave comes down from the top.
This one is found in Mission 8 inside the Leviathan's stomach. It is found under the ship behind some wooden planks you have to break. It is portrayed as a large blue glowing tablet. This secret mission has to be accessed and completed before the Ignis Fatuus is obtained, or the tablet will only glow a dull blue in the dark and becomes inaccessible.
For first timers:
It is more advised to use a maxed out D.T. However, it will waste out large amounts of Devil Stars since you have to replenish them. Holding and releasing it to form a fully-charged DT explosion, this one is enough to kill the enemies. Taunting after the DT explosion helps you regain some of your DT gauge, allowing you to do more DTE. Alternatively, returning to the mission after unlocking Kalina Ann will easily blast away the enemies.
For experienced fighters:
Use a fully-charged Volcano at the middle of the elevator. Release it when the enemies fall on the elevator. You can also use Kalina Ann and stay at the edge, but assume that you will not be hit or else you will fall back.
Use Spiral Swords at the middle while you are doing a Force Edge combo. Or also use Level 2 Judgement Cut. To do this, go to the middle and hold. When the enemies DT (you can see their activation as flashing part of purple spheres), quickly release the buttons, and skewer them.
If you get frustrated by this Secret Mission, don't worry because there is a "cheat" that exploits the distance limitation of enemies. As Trickster, position yourself at one of the corners and jump, Air Hike, then Wall Hike to run up the support column. This should put you far enough above the platform to force the Hell Prides to disappear. As Dark Slayer, position yourself at one of the corners. Since Vergil can't Air Hike, you must use double jump, then Trick Up. Remember to face the enemy and lock-on to Trick Up. Repeat this process four times and you are done.
Alternatively, you can simply pass this mission, then return to play it in Heaven or Hell Mode. In this difficulty mode, it is obvious of what you need to do: simply do anything to damage the Hell Prides, as they will die instantly. However, watch out if they managed to land on the elevator and attack you, as you will also die instantly. A good strategy is to use Gunslinger with Ebony & Ivory's Rain Storm. Since the Prides are clustered, all of them will suffer from the hail of bullets. Another good way also utilizes Gunslinger, but with Shotgun's Firework. Simply stand at the center of the elevator while keep firing Firework, and the scattered shots will create an impenetrable sphere that protects you while killing the Prides as they approach.
As Vergil, as soon as the damage wheel is fully lit, stand in the center of the elevator and use Spiral Swords (do NOT use advanced Spiral Sword's techniques, as Sword Storm can only kill one Hell Pride per execution and do not use Blistering Swords, either, as the swords may destroy all the Prides in a wave with a single execution, but you need to use it several times to get atop the elevator shaft). As the Hell Prides approach, they are obviously immediately butchered by the sword barrier. This will barely damage the Summoned Swords, as the Prides barely deal any damage to them, so you will not need to summon Spiral Swords for the second time.