Backstory:
Not everyone thinks the same about everything and even though most of knights want to get out from Cradle alive, there are few those believe otherwise. Three of these decided to turn their backs to Spiral Order and try to stop all efforts to reach the core and obtain its power. Even though it makes us sad to strike down our own knights, Orders mission is clear. Go their base and finish them

Levels:
I am placing following depths into T3 as T2 already has two bosses.

Depth 24 Blackstone fortress: entrance
Depth 25 Blackstone fortress: Obsidian shield
Depth 26 Blackstone fortress: Ruby blade
Depth 27 Blackstone fortress: Jade bat
Depth 28 Blackstone fortress: Final showdown

Blackstone fortress would be made out of, well, black stones. Torches would give out nice light effect and make it remind more of dungeon. Different thing in this boss area is mainly the fact that you will fight FOUR separate boss fights. Yes, four. Please don't start raging on me yet and keep reading to end.

Entrance level: Big gate at start, the place is fortress. Inside you go and fight multiple enemies, it does not matter. Just add something that could pop out in fortress. (Mecha knights, turret like enemies, few slimes...)

Obsidian shield: The first ACTUAL level and also the first fight. At the end of floor there would be big square shaped room, which has party button at the entrance and gates to prevent going further. There would also be two heart boxes before the match so that you could heal bit. After activating the button, you would be facing first betrayer, Shiram. More about fight against him in fight section.

Ruby blade: About same as Obsidian shield, except this time boss is Ashura. Again, more about him in fight section.

Jade bat: Same as above, boss is named Gon.

Final showdown: A big circle like room reminding lot from those from arena. Heart regenerators at start before match, hope you are ready.

Actual boss fights:

Shiram: Shiram is knight wearing customized plate armor which is colored deep black. As weapon he has spear (which looks lot same as one Slag walkers have). He also has big shield, which is looks like it would actually be a big plate from armor. As you start the fight, he will slowly turn around and say following: "So Order did not heed our warning... I am sorry, but I must dispatch you."

Shiram has resistance against piercing, takes normal damage from shadow and increased damage from elemental. He has also long negative status against shock and fire statuses, so those should be used. As the fight starts, he will slowly move towards one player he has taken as target and try to attack him. He is slow, so you can pretty much out speed him even if you would be wearing armor that drops your speed. His attack are also slow and give obvious warning from them, so target can easily evade them. But because of his slow movements come from his heavy armor, it should be obvious he can take large amount of beating.

Attacks:
Swipe: Shiram swings his lance in same motion as Leviathan blade. (deals piercing damage and stun the target)
Throw: Shiram lifts his lance above him and throws it at his target. After attack, lance is stuck into ground and he will go to retrieve it. (deals piercing damage and can stun the targer)
Shield: Shiram lifts his shield up. Players must break it down same way their shields can be broken. If shield is broken, Shiram needs to wait twenty seconds he can use it again.

Ashura: A Knight with two handed weapon. He has thrown his shield away so you wont be seeing it. He has red leather like clothes and his sword is bright blue, almost as ice. As the fight starts he will say: "We do not belong to Cradle, so why do you fight so hard?"

Ashura is about same speed as normal knight but his attacks hurt a lot. He resists elemental damage, is neutral against piercing and takes extra damage from shadow. He has negative statuses on curse and poison so use those for your advance. Even though Ashuras attack will hurt and may come as surprise, he has kind of cooldown after each attack, which is spot you should deal most of your damage on him. Move fast and you should be fine.

Attacks:
Swing: Ashura swings his sword and knocks poor victim back. (elemental damage)
Impale: Ashura jumps skyward and then comes down to one spot. Spot is marked with same kind of mark you get as warning from roarmulus twins rockets. (Elemetal damage and can freeze target)
Charge slash: Ashura runs away from players and starts charging his sword for attack. If charging is canceled, he will instantly swing his sword instead. If he managed to finish charge, he will unleash Glacius charge attack. (elemental damage, chance to freeze)

Gon: Knight who looks lot like assassin. Gon wear ninja like clothes and has shield which looks like bat. His sword is kind of dagger. As entering the room, Gon will say following: "...Die."

Gon moves fast, so you will have hard time hitting him. His hits wont be doing lot of damage but there will be multiple of those incoming. Gon resists shadow, is neutral to elemental and takes extra from piercing. He is also vulnerable to ice and stun statuses, wich should be used because they remove his speed advance. He is also fragile and will lose very fast if you can get multiple hits through.

Attacks:
Rush: Gon attacks in same pattern you see cutter being used. Do not try to shield this, as hits will come in fast. (shadow damage, chance to deal poison)
throw: Gon throws random vial at his target. Depending on vial, different status changes are possible (not curse though)
Tele slash: Remember alpha wolvers dig? This is same, except there isn't as much of warning before the attack.

Final showdown: You bested them once, so they retreated. Now they are back and you will need to face all three SAME TIME! Earlier fights may have seen easy, but do not underestimate them this time. At start of battle, Shiram will say following: "...You are strong... We honor you, but we can not give up. We shall fight for this world, to the very end!"

All three are up: All move around arena and sometimes one of them goes to middle. That one is the one who will be attacking, so be prepared against his attack. Keep hitting them, until one falls. Depending on who you defeat first, you will be facing different kind of battle.

Shiram and Ashura: They will both start chasing one player. Something Ashura will dash forward and try to grab (aka freeze) one player. If this is successful, Shiram will try to throw his spear at the player. Captured players can be rescued by hitting Ashura while he is holding the player.

Shiram and Gon: Gon will disappear and soon appear next to Shiram. They will go after separate targets and they will try to remove them one by one.

Gon and Ashura: Both will start rushing around arena and trying to deal as much damage as possible.

Again, defeat one of them to move to last phase.

Ashura: Basic Ashuras match, except he will have more health
Shiram: Basic Shirams match, except he will do more damage
Gon: Basic Gons match, except he will teleslash more often.

Death quotes:
Gon: "I...Have...Failed..."
Ashura: "Sorry..."
Gon: "So is life..."

After defeating any of them in their solo matches, you will reach the lift and can pop open 4 treasure boxes and 2 heart boxes. After the final showdown, you will be rewarded with "Core shard(s)". It will have following description: "A metallic shard that seems to be from core. It does not contain any power left in it though.

Possible items:
Jade bat: Shield Gon used. Has low health, medium normal def and medium shadow def. Grants movement speed bonus med. (4* item) Description: "This shield seems to be pulsing energy. It is memento from Gon, one of betrayers."
Obsidian Shield: Shield Shiram used. Has high health, high normal def and normal elemental def. Grants high res from fire, but gives movement speed red low along with attack speed red low. Description: "Heavy and sturdy shield. It is memento from Shiram, one of betrayers."

Comments and suggestions are LOVE