My suggestion is a new (possibly boss) stratum
These levels, (Maybe clockworks, Maybe event, who knows) is called Temple Of The Masters. The objective is to mentally and physically challenge you like never before, offering you every enemy, every theme, and maybe even every bosses if you'd like to push it. The temples would take a bit of time to accomplish, And, No enemy give you any payout, There is no rewards at all but one at the end. The Temple should be FREE to enter, however, you get only ONE chance every 24 hours, and no reviving. you die, you loose. end of story.
When you reach the end of the Temple Of the Masters, you reach one final battle in which your knight must fight the Master, I'd imagine a Knight in a black and white colored Azure Guardian, switching between the weapons: Leviathan, Nitro, and Valiance based on what weapon you're using. So if the Master's target is you, and you're holding a gun, He switches to Valiance. If he switches target to a Bomber, He'll use Nitro, and for sword he'll use Levi.
Defeating the Master will give you an artifact, and, a Trinket. The trinket will be called 'Weapon of The Master' and it's description will be: "A Master's Weapon is not an object, but the ability to use an object" which will offer a Medium attack, Charge time, And damage bonus to all weapons. and CAN NOT be unbound or sold. The Weapon Of The Master item is strictly for those who defeated The Master alone.
Another idea for Weapon Of The Master instead of medium bonuses, Could be a Ability increase, Effecting each weapon differently for example, a Leviathan would spin twice on charge, DA/GF have extra projectiles, Smash weapons having more rocks, Brand weapons having longer range. While guns having extra ammo before reload, and bombs having a increased blast radius.
I imagine the Temple Of the Master to be like really long arenas. Each depth being a new Monster category, Each room being a different element to it. So by the end you've fought every monster of every status type.
Lastly, you need Tier 3 access to attempt Temple Of the Masters, And once completed you may still play it, however will not be able to obtain the reward twice.
I would imagine the layout as 30 layers of rings, one for each monster and element family with the party starting in the middle circle. They proceed outwards from different rings. When The party completes the ring, the next ring is rotated at high speeds and the screen flashes white, revealing the next arena on a monitor, and the next ring can be accessed. The background also changes.
Also, you may buy a checkpoint for 750CE, so you may continue later. This means other players need the same checkpoint to continue.