This is an idea I just recently came up with. I thought I would share it to show a potential next step for the story that GH may or may not ever continue, let alone finish.
The story so far
It's been a month since your squadron returned from your expedition to the Core. Since then, the Core has laid entirely dormant; there has been no sign of the Alpha Squad nor Herex.
Spiral HQ has decided to continue exploring the darkest depths of Tier 3 for more clues; all they have found thus far was the long thought-to-be-lost Starlight Cradle sector, and this proved to be a dead end.
In the meantime, mysterious seismic and radio activity appeared from the Royal Jelly Palace. You were sent to investigate, and discovered the castle was under Trojan occupation, headed by a powerful commander who claimed the entirety of Cradle property of the Legion of Ur. You barely managed to subdue him; interrogation revealed that the Legion was using the Palace for a strategic advantage in their upcoming conquest of the ultimate prize, the Core.
As if on cue, the Core has opened yet again. Lieutenant Feron suspects the Trojans knew this would happen, and has sent an emergency order calling all knights to defend the Core, headed by a special ops team you have been selected for.
Prepare for the worst and take the fight to the Legion.
Gameplay stuff-
New environmental gimmicks
Catapults - Fundamentally the same as the artillery strikes in levels like The Collector, they strike a certain tile and you have to get out of the way. Iron catapults simply hit once with massive normal damage, while the explosive ones are loaded with bombs.
Spinning Blade Totems - Basically cylindrical Misery Blocks. These move on a set track, hurting for heavy damage if you don't get out of the way.
New enemies
Bomb Trojans - They always hold massive bombs that they toss in an arcing motion, but they can also leave them on the ground like traditional SK bombing. They look just like normal Trojans but have a greener paint job and don't bother with carrying a sword.
Red Trojans - Trojans with a sword in each hand. They can be hit from the front for reduced damage, but good luck hitting them there, as they're far more agile than a regular Trojan. Rather than constantly swinging at the ground, these Trojans prefer to take quicker slashes with a bit less telegraphing than their counterparts.
Tier 4 Trojans - Straight from the Underworld, instead of a traditional stone horse face, they have a cracked horse skull with what appears to be horns forming where the ears would be.
Cursed Guards - When the Firestorm Citadel fell, many of the surviving Deadnaughts fled with the Trojans to the Underworld. They were soon sold into slavery and forcibly drafted into the army. A long stay in the Underworld has left them with pure white bones and purple armor courtesy of the Legion Army. Despite their name, they cannot deal a Curse status, but they hit for massive Shadow damage.
Now, on with the show.
Depth 28: Preemptive Strikes
The Trojans knew that Spiral HQ was on their way to rescue the core, and have sent a battalion to intercept your squadron. You have no choice but to rip and tear through them in your race to the elevator! The Legion brought out the best they could on short notice: Iron Catapults and Misery Blocks will be the only resistance you'll find apart from the monsters themselves.
The level is normally short but there are some detours you can take to assist struggling NPC knights in battle. They can give you rewards if you defeat the enemies attacking them.
Depth 29: Fog of War
This is majorly a cutscene level. As you reach the Core Terminal, what else awaits you, but an angry army of Trojans fresh off the elevator to the Core? When all seems to be lost, backup arrives in the form of a dozen or so Spiral Wardens and Mecha Knights led by Vaelyn. Lieutenant Feron contacts you asking for you to hold off the Trojans for just a minute while he executes Plan B. A massive battle ensues; you don't have to win, just live.
Eventually, Plan B shows itself: a massive Mist Energy cannon mounted above you. A small cutscene displays it charging energy and shooting a massive blast into the crowd of Trojans, wiping them off the map. Feron has given you a clear route to the next elevator, allowing you to start a new level.
Depth 30: Next Step
Now, you make your way back into the Core to take the fight to the Trojan invaders. They've set up shop nicely already; Spinning Blade Totems and Explosive Catapults are at every turn, usually with a few Red Trojans and their bombing counterparts not far behind.
Near the end of the level, you reach the last battle room, triggering a cutscene of a conversation between two Devilites that are behind the gate; they get a phone call from their boss to activate Protocol 76, and that they know what to do. The Devilites draw some runes on the floor and activate a few machines that rip open portals to the underworld, bringing forth a cadre of Tier 4 Trojans and Red Trojans, emboldened by Healing Totems and Swarm Seed.
There are more detours in this level leading to caged Recon Knights, who this time have a chance to offer Keys to a few hidden treasure rooms, Radiant Fire Crystals in sets of five and single Sparks of Life.
Depth 31: Final Step -- Confrontation
Besides new Tier 4 Trojans, Cursed Guards, and several new enemy formations, this is largely similar to the previous floor until the final room, a dead end where the Swarm takes complete control. Void Gel, Gremlins and new Retrodes fill the room in big groups, similar to Slags in Firestorm Citadel. At the end, the Swarm Monster that joined with Herex at the beginning of Dreams and Nightmares appears before you, dissolving the wall in front of you to reveal a bridge to the exit.
If you look hard enough, you can also spot a switch; by hitting it, you reveal another hidden path. Besides treasure boxes, on this one you find something different, a lore secret. Scattered bits of metal lead you to what looks like a mostly intact Spiral Warden chest plate in the middle of a big empty room; checking it reveals a dialogue:
"Bits of this armor were scattered all across the way here, as if the wearer was dragged here from another location or vice versa. Its composition is pristine; only the most prestigious elites would ever be granted such."
Depth 32: Left For Dead
At last, you arrive at the boss. After the usual heart refresh tiles and boss hint module, you're tricked by the Party Button failing to activate the boss. You walk through several empty rooms with Legion of Ur flags mounted on the walls and gates closing behind you, the screen itself rumbling with its ominous heavy steps. At the final room, the gate behind you topples with a thunderous crash, revealing the boss; he was following you the whole time.
The boss, General Iliad, bears a vague resemblance to Vanaduke in his upper body shape and features. His body is bisected at the waist; the femur down is completely skeletal except for some Swarm tendrils holding together the broken parts of his legs. Black, jagged rock covers his upper body, like armor, which is pierced by many Dark Matter shards as well as a mysterious gray crystal, and many blotches of the Swarm. Finally, he fingers on the right hand are all covered in shadowy retextures of various in-game swords that serve as claws, his main method of attacking you in this fight.
Iliad isn't easy to beat. His only weakness is to strike him with a Shield Bash just as he's preparing an overhead swing or about to perform a ranged attack, though the latter must be done from behind or he'll counter. Time your bash wrong, and it could cost you nearly your whole life bar. When he gets knocked over by the bash, one of his main crystals will be exposed: one on the back hidden by a torn cape, and one on the palm of his bladed hand. They both must be destroyed to win the fight, and they both have tons of health and resist all but Piercing damage.
Iliad has many attacks besides the regular hand slashes.
Burst Charge: His version of the Brandish charge, forms several explosions in front of him.
Sidestep: Sometimes he can step right out the way of your attack if he's standing still.
Phantasm Orb: A large ball of shadow that flies forward and bounces off walls. It automatically disappears after 10 seconds but can be destroyed by any projectile attack from a Battle Sprite. Leaves him open to a Shield Bash.
Murder Rain: He points forward, red circles appear on the floor for a moment and purple acid rain comes down, leaving a damaging Elemental residue for a few seconds.
It takes quite a long time, longer than Vanaduke, but Iliad eventually falls.
Don't think it's over yet, though. Just when it seems like you should be getting your tokens, the Swarm suddenly overtakes the area and a blue-violet lightning bolt crashes into Iliad's corpse, fading the screen to white and triggering the level complete screen.
Depth ???: In the Land of the Living
We resume right where we left off, except the scene has changed from the pure white Core to a twisted, entirely otherworldly dark valley. Iliad's body sparks and glows with energy before he stands up, his skeletal lower half completely disintegrating and leaving the upper body floating like a ghost.
Once more the fight begins. You'll find Iliad seems to be totally invincible, parrying or just blocking every one of your attacks. But as you charge your attack, loose Mist Energy in the air will collect in your body, turning the charge meter blue and increasing your running speed. If you let go of the charge, it will turn into a massive, blisteringly fast bolt of pure energy that can stun the boss, even without having to wait for an opening. By performing several of these attacks in quick succession, Iliad's energy dissipates and he's wide open.
In the traditional fashion, Iliad dies with an explosion, leaving not just tokens and crowns, but also a portal back to Cradle.
New Brinks rewards
Rust Talon- A sword with a brand new gameplay style based very loosely on Iliad's knife hand, not nearly as cool (that can be saved for a prize box promo or something). This is the 4 star model, it's missing a few fingers and the blades are rusty as the name implies. It does Normal damage with small Poison; there are two five star upgrades, one to make it pristine and deal much more Normal with Piercing damage, and one to make it a lot more rusty and keep Normal damage while buffing the hell out of the poison.
Longshot Bomb- Based loosely on the Trojans' bombs, it can be thrown a distance as the name implies, obviously with balancing to keep it from being a new RSS or something.
I like the concept. It's always cool to explore another dungeon. My only concern is that it seems like it might be too hard (though that's probably just the descriptions talking), since difficulty is only good until it becomes incredibly frustrating or seemingly impossible (incentive to buy energy possibly, but not even SK is that evil I'm pretty sure).
(I'll post down any other Brinks reward ideas I think of. Two prizes seems a little lacking.)