As confused by the Halo Infinite ending as I am? If you're looking for a game with a straightforward and well-rounded ending, then Halo Infinite isn't what you're looking for. Granted, this is Halo Infinite we're talking about and the ending sets the scene up for DLC perfectly, but prepare to be just as bewildered and confused as you have been the last few years. There's also a tasty post-credits scene that sheds a little more light on what's to come, but not by much.
If you're not interested in reading about the last few hours of Halo Infinite or knowing what's in the post-credits scene, then consider this your spoiler warning.
Ready, Spartans? Let's go.
Halo Infinite ending explained
Ignoring capturing FOBs and hunting targets, Halo Infinite's campaign wraps up exactly how you imagine it will—with lots and lots of bullets. You'll need to fight three bosses and three rounds of painful 'training' to complete the campaign which, as expected, is an absolute ballache on Heroic and Legendary difficulties.
You'll eventually end up in the House of Reckoning, where many UNSC marines were slaughtered by the Banished. First is the training section where Escharum has you fight enemies in basic and advanced training. You'll fight Grunts, Brutes, and some special red-eyed Hunters, so try to be methodical about your approach. The upside is that there is a tonne of weapons and gear lying around, so you shouldn't run out of ammo.
After that, it's on to one of three boss fights: the Elite Spartan Killer, Jega 'Rdomnai. He has a big red energy sword and a smaller energy weapon that will definitely mess you up if he gets too close. The tagline for this mission says "Survive. Just survive." which tells you everything you need to know. He also goes invisible for most of the fight, though you can hear his footsteps and breathing, as well as see his outline shimmer when he's close.
Your best bet is to equip the likes of the shotgun or Needler so you can fire projectiles rapidly at him to highlight his position, as well as use your grappleshot and grenades. You can melee him, too, but that's obviously a bit risky due to the dual energy swords. After he's dealt with, it's on to fight the Banished War Chief Escharum.
Hitting him while his shield is active hurts Echo 216, so the Weapon will inform you that you need to hit energy relays around the room. You need to destroy the orange relays then inflict as much damage on Escharum as possible before his shield regenerates. After all four have been destroyed, he'll begin wielding his big ol' hammer and move at speed to catch you. There are a few rocket launchers hidden around the room as well as a shock rifle, so use your grappleshot to evade him and take your shot.
He'll give you a stirring monologue when defeated, then it's off to fight the final boss: The Harbinger. She'll teleport around the room and, like Escharum,be shielded for the majority of the fight. You'll face some difficult enemies in the arena, including several heavily-armoured Brutes with gravity hammers, but once the adds have been cleared you'll be able to fire at her.
I found the Needler to be particularly effective against The Harbinger, alongside the Bulldog shotgun and grapple-melee. Again, after she's defeated, there'll be a monologue and Chief will return to the Pelican.
We also get to learn what happened to Cortana—and how she's connected to the Weapon. The Weapon is a perfect copy of Cortana with some key bits removed to make her as dissimilar as possible. In the end, Cortana sacrificed herself to destroy the ring and delay the Banished and The Endless' plans. The Harbinger is one of The Endless and it's unlikely we've seen the last of them yet. The Weapon hints that she might want to take on Cortana's name, but once the credits rolled, she was still called The Weapon, so who knows?
Halo Infinite post-credits scene
After sitting through/skipping the credits you'll be treated to a post-credit scene. Surprise! Atriox is actually alive and still hellbent on summoning The Endless, an enemy supposedly more deadly than The Flood. Killing The Harbinger seems to have triggered their arrival and small motifs showing The Endless' icons start spinning in a floating structure, which I took to mean they're on their way. Atriox remains as angry-looking as ever, so hopefully, we won't be waiting long to see what happens next.
Once the campaign is complete, you're free to explore the open world, capture FOBs, and do whatever else you want. Have fun, Spartans.