Fun fact:  All of the Astartes soldiers and priests suits are completely sealed and 100% sound proof from the inside.  So, when you hear the priest screaming through the helmet, that tells you just how loud he was actually screaming.

not seeing anyone else here commenting it, so i’d just like to let yall know, this entire animation series was done by ONE person, who was now officially hired by WH40k.

From the Astartes video:

The boarding craft is a Caestus Assault Ram, named after the ancient Roman fist weapon, it's fitted with twin-linked Magna Meltas (giant microwave guns) to literally burn a hole into the target craft's armor plating and disgorge it's even deadlier payload: up to two squads of Astartes.

That armour is Ceramite, a ceramic alloy, able to withstand many, MANY things that the galaxy throws at the Astartes. the multi-las trestle weapon the rebel Guardsmen were using only succeeded in burning off some paint. The armour is called "Power" Armour because it's got mechanical servos augmenting the strength of the wearer, powered by the 'backpack' generator on it, giving the Astartes much greater strength and speed than even their enhanced physiology can provide. They can sprint upwards of 55mph, it has been said of them that nothing that big should move that fast.

Boltguns fire .75 caliber rocket propelled mass-reactive shells (meaning they explode when surrounded by mass, aka a body). Plasma pistols are more specialized and usually given to squad leaders and sergeants who will know how best to use them effectively, as they're usually only good for a few shots before overheating (and possibly exploding).

The Inquisitor is a psyker, able to use his mind to tap into the Warp and essentially use the energy within to "cast spells". He's psychically listening in on the orbs' conversation, but when he warns the Captain (denoted by his white helmet and laurel) to "RECALL THEM IMMEDIATELY" he loses his focus and gets possessed by a Warp entity. The Marines react swiftly because allowing a possessed psyker to live will let the daemons of the Warp use him as a living conduit to manifest in realspace.

Secret Level:

A Space Marine's duty is to the Emperor and their Chapter. If a mission calls for sacrifice, they are willing to pay that price to safeguard the Imperium. "... and they shall know no fear."

They're fighting Chaos cultists who worship Tzeentch, the Chaos god of change and knowledge. This is why they're all spiky and covered in skulls and flayed skin and shit. The Chaos Sorcerer (who appears to have mutated or bonded with a Horror of Tzeentch) uses his powers to prey upon their fears, but that shit don't work on Titus, for he has purged himself of fear. Tzeentch is the god of psychic power so it's common to see this type of mindfuckery being used on anyone opposing his forces.

The psyker-in-a-can is to provide them with a psychic barrier while they complete their mission, mainly because Tzeentchian cultists and daemons are more apt to use sorcery against them than followers of the other Chaos Gods, who are more apt to use physical force (especially those of Khorne, Tzeentch's opposite).

The pieces of paper are known as purity seals, blessings awarded to warriors by the company Chaplain in recognition of their devotion and uncorrupted nature. It's not proven but some psykers believe that affixing purity seals to their headgear can ward off possession.

30:12 Chaplain verse:"We straight gasing cutting straight to the brinks" bolter unloads
Average blood angels boarding

you need 1 space marine to conquer a city.  10 to conquer a country and 100 to conquer a planet   written in a 40k book

I love how he says villian is OP when it's like an unnamed minor demon at best. Watching people discover 40k and realized how hopeless and scary it is, is one of my greatest pleasures.

32:08 "I see god" as they walk into darkness

31:46 I've seen timings in my life, but this one hits different HOOOOOOLLY

Also to explain why Metaurus got affected by the sorcerer. His fear is that he is afraid Titus was corrupted by chaos and how powerful he would be if he had. Due to the ending of the first space marine game there were accusations of him being corrupted by chaos (cause no normal marine could have survived a direct interaction with an artefact he held at the end) . Which is why you see a chaos version of Titus just as hes being stabbed. Dont know if everyone caught that. As Metaurus oversaw his recruitment.

The secret level episode converted me to 40k on the spot when it came out. Right away I started listening to lore podcasts (40k lorecast) and other YT videos. Im still astounded how I never got into it earlier

Best thing is he paused the two vids individually breaking them apart a little bit, but in doing that he landed a perfect sync 31:49. It was god tier and hilarious !!

31:19 I died here, and then again at the drop.
- WE GET BACK IN BLOOD. YOU SEE IT?
I REALLY DID THIS. I AM REALLY HIM. PUT THE WHOLE BRICK INTO AN EMPIRE. STOP PLAYING WITH ME.
I HAVE NO SYMPATHY. I LIVE FOR THIS SHIT. THIS SHIT AIN'T NOTHING TO ME MAN. I AM NUTS WITH IT.
HA-HA. MY MONEY LONG. MY POCKETS DEEP. NO POCKET WATCHING IN THESE PARTS.
WE STRAIGHT GASSING CUTTING STRAIGHT TO THE BRICKS.

Legendary moment of the internet.

30:12 I have never seen a more insane timing than this one, actual Cinema.

"Die well brothers" was not to the dead marines. It was to the ones still alive. They were sending an orbital strike on that position once the link was reastablished and they could target again. It was a one way trip.

30:13 to 32:15 is officially the clip of the year! I'm in tears man

4:45 This dude had 3 people saying "Psykers" with one dude misspelling "Psykes" in the middle of them, and he still read the SINGLE ONE with a spelling error. Goddamn.

31:49 It fits so f-ing perfectly...

Bro says at 0:40 "Do you think this will be the future ever?" I hope not xD Imagine living in the 40k universe bro. Im good xD

31:40 Hahahaha this absolutely fuckin LEGENDARY !!! hahahahaha

The chat didn't do space marines justice when describing them as super soldiers. They're so modified that they're not really even human anymore. 3 lungs, 2 hearts, they can literally spit venom. Their bones are hardened with a substance similar to their armor, and their rib cage fuses into a single solid plate, basically giving them a second layer of armor. They can even eat the brains of their enemies to take in some of their memories. And those are the old school marines before their primaris upgrade.

I don't play the tabletop game anymore so don't really follow the lore much anymore, but I always loved reading up on it back in the day