Hit the marker on the helipad to start. This can actually be a little tricky to get to- you can use the ledges and passages in the alley way to jump up, but you may find it easier to just take the elevator in the Lucky Seven Casino to the roof, and jump on over.
Doc Babylon starts tearing apart reality which... isn't good. Drop down to you vehicle, and make for the rift. Ignore the lightning blasts- they aren't really aimed at you anyway.
The road markers here can be a bit confusing, but you will need to off-road in the dry riverbed a bit before a lining up a jump into the rift.
You arrive on the other side without your car. It's probably fine. Hop skip and jump your way along the fractured reality, until you encounter some goons, outside an alterna-real Char-B-Q. Things escalate quickly here, from mere helltroopers to blitztroopers, boombots, and pot shots with a space laser.
Still, nothing you haven't seen before, and you do have some room to flee for safety if find yourself getting surrounded. When the last wave, headed by a blitztroooper commander, is downed, jump into the next rift.
The new arena, overlooked by an August Gaunt statue, phases through helltroopers, swarmtroopers, then snipetroopers, headed by a snipetrooper commander.
When resistance is quashed, it's into the next rift.
The new stage is another wedding revisit, and progresses through helltroopers, blitztroopers, and bufftroopers, before serving up swarmtroopers, helltroopers, and shocktroopers.
After the shock troopers, more helltrooper reinforcements arrive to support half a dozen snipers, and then a final wave of grunts led by a Tanktrooper commander.
With this last wave of mass carnage behind you, leap into the final rifts that lead to Damocles.
Once inside, approach the giant crystal to trigger an awful lot of cutscene villainy.
You'll now face all the game's previous bosses, attacking in pairs. Not any of their stages, just the bosses themselves. If you've been raiding outposts and stopping doomsday devices at the higher difficulty levels, you've probably already encountered these avatars.
The first set up is Hammersmith & Gaunt.
Focus on taking down Hammersmith first- he's weaker than Gaunt, and while his attacks are clearly telegraphed, they're also longer range, increasing the chance of badly-timed surprise later. Joule's turret and slow/stun/immobilze debuffs are all good ways of keeping Gaunt out of your hair while you whack his partner. Afterward, take down Gaunt as per usual. Scheherazade remains an infinite well of DPS, for example.
Similar tactics apply to the next pair up - warbot Aisha and Steeltoe.
Despite the power of his shield bubbles, Aisha's the primary threat here. Take them in order, as you did their predecessors, saving Steeltoe for dessert.
The final fight is barely that. In the first phase, Dr Babylon will levitate and hurl fire at you, while you attack from a distance (shades of your first meeting).
Do enough damage and he retreats, leaving the field to Ariadne. Hang as close you can to the big crystal, egging her on with attacks until she snaps back, damaging the crystal itself.
Repeat this cycle twice more and then, when Babylon retreats for the last time, attack the crystal yourself.
And that's the last trigger you'll need to to pull for a while. A final cutscene closes the story (sort of), and the credits roll.
You do still get XP, rewards, and mission completion afterward.
Still, the game's not over yet. You can still explore the city, complete outstanding missions, tasks, and contracts, and capture LEGION resources. You can also, through the TAB menu, replay any of your completed missions for fun and profit.
You can also unlock more Legion Tech and Elite tech, explore the high-high difficulties, and even (if you must) find all the hidden crystal shards around Seoul. Game on, Agent.