What I mean is what chapters would you be surprised to see. As an example, I know not a soul expected to see the Masters of Protelus or the Angels of Fury at Armageddon. One that I'd like to see is the Imperius Reavers or the Dark Hands.
I will preface that White Dwarf chapters are dubious in their canonicity, with the soul exception of the Penumbral Talons, since they appear on Armageddon.
The Imperators are from a pre-ultima founding and unknown origin. Created by GW employee Christian Byrne in WD 352 UK. You can kind of make out the Chapter Badge, which looks like a sheild with the Eagle Warriors Wing thing.
The Black Scorpions are from an Unkown Founding and origin. They were one of the many chapters who participated in Fall of Medusa V campaign. They specifically fought in the Battlezone Edethor. By Campaigns end the Commander of the chapter's force had earned an Imperial Laurel. But their is some contradictory information as there was another group called 'Black Scorpions' who were a Chaos Warband led by the Chaos Lord Desek.
I think they are Chemical Warfare specialists. Their parent chapter stays unknown, but it speculated among the 2nd founding chapters that they are a Death Guard warband. They were founded early but unlisted. Their homeworld is called Ar-Keeto, an arid and toxic desert in a similar vain to Baal and they have an Arabic esthetic. A couple years before the Medusa V campaign, the 7th company went rouge and turned to Chaos, specifically Nurgle. The company was lead by Khayri Desek, and fell after an redacted event, and subsequently classified as 'Excomunicate Traitorous'. The chapter's main goal in the Medusa V campaign was to hunt down the splinter. The response force, led by Zulfaqar Osvas and they failed as Desek received a trophy from the chaos gods. After the Great Rift opening, they have become a favorite for Cawl's Research as they have a "very loyal gene-seed".
The Heralds of Ultramar are from an unknown founding and very likely Ultramarine successors. and they have no lore.
They could be like their name sake of a 'Herald' and act like diplomates, in charge of convincing planets to join the Imperium. Or they could represent Guilliman's political acumen while the Ultramarine represent his war skills.
The Emeralds of the Imperium (EotI) are from an unknown founding and parent chapter. They don't have any lore to speak of. However they were created by Matt Meek and they appeared in The Citadel Journal 24.
I imagine them being the propaganda marines, like they are the ones the public sees the most. Being called the "Emeralds" as a rich material sported by royalty and fame. So they act like a stuck up version of the Ultramarines.
The Storm Hawks are from an unknown founding and they are an alleged Raven Guard successor. It's only piece of lore that I've found is that their Homeworld is called Zephyr, located in the Segmentum Obscurus. By all accounts they have no relation to the (now legends) Storm Hawk Interceptor.
Despite their no relationship with the Interceptor, I do believe they are some of the best pilots of the Space Marine Chapters. Making them highly coveted for Deathwatch service to pilot the Corvus Blackstar. Or they are proficient in any type of vehicle, but as GW purged most First-Born Space Marine armory, I'd wait to build an army.
The Space Rats hail from an unknown founding and origin. The Chapter was left to guard a reconquered planet from the Eldar, they were attacked by an intelligent, twin-tailed rats and barricaded themself into the interior of the planet. Unknown to them, they'd been isolated by a warp storm and for millennia their messages weren't received. When help arrived, they found the Chapter's gene-seed altered, giving the Space Rats improved infra-vision and a telepathic ability. The Space Rats was created by Sławomir Zajączkowski, from Poland, for the UK WD's Create A Space Marine Chapter Competition. It won 8th place and was named in WD 304 (UK) and featured in Best of Chapter Master.
The Black Vultures are an Ultima Founding successor of an unknown parentage. Unlike most chapters of White Dwarf origins, they have a little to chew on. The chapter is full of meticulous planners, and patiently marksmen. This led to interactions with more aggressive Chapters, like the SW and BT. The Black Vultures have established ties with the Mechanicus and will occasionally undertake operations by Tech-Priests. During these missions, in which members of the Mechanicus will retrieve relics, the Vultures secure assets that benefit the Chapter and help them receive support from Forge Worlds. Because of these links, they've receive preferential treatment. The Chapter interacts with the homeworld's population like the Ultramarines do and through their proximity, provide some protection for these citizens. This has allowed the world's System, to develop as a trade hub.
The Remnants are from an unknown founding (Pre-Ultima Founding) and of Blood Angels heritage. They were created by the GW employee John Bracken and were featured in WD 395 (UK) and WD 398 (UK). They have a very unique color scheme for a BA successor of Purple and Gold which is slightly heretical, but its quartered so we all good.
With the name of "Remnants" I could think they were a BA successor of an almost completely destroyed for some reason. Or they were a collection of Blackshields from the traitor legions who stayed loyal and strained elements of the BA, specifically the Blood Angels and Emperor's Children.
The Panthers are from an unknown founding and origin. They don't have lore in the traditional sense, but what they do have is inconsistencies. There are supposedly 2 separate chapters with the same name; one in WD 210 UK and in chapter approved 2001. As neither has lore both or none have lore.
In the meantime I will give a little fluff. They are a Raven Guard successor from a later Founding, but before the Ultima. These Marines were known as crude Stalkers. Hailing from the tribal world of Folida, where the Emperor is considered A Forest God and the Panthers his divine wrath. To curb this chieftains offer their young to them as an offering. They are in my mind the RG equivalent to the Mortifactors. One unique thing is that they are known to use Folida's large wild cats, known in laments terms as Folida Panthers, as trackers akin to the Fenrisian Wolves of the Space Wolves.
The Ice Bears are from, presumably the Ultima Founding, but an unknown origin. Created by Ashley Lowe, a GW employee. A Primaris Chaplain was showcased in a WD September 2019 article.
I image that they are hazardous, winter environment specialists. I also think they are really distant successors of the Salamanders. They could have this terrifying appearance in winter storms with the red eyes, but when you approach them they actually really nice guys.
The Shadow Hawks are from an unknown founding and origin. The chapter had been recently spotted fight Eldar at some point in the galaxy. The Chapter’s 3rd Company turned traitor in The Cruach Mhorn Massacres (292-304.M39) After facing censure for the Massacres, The Company later became the Slaughterkin Warband. They also participated in the First and Second Punisher Wars. Finally the Chapter was tasked to aquire the pupa form of a Vespid Leader by the Ordo Xenos, the Chapter failed and the Ordo isn't happy.
As their only model is a Devastator (RIP) I imagine they appear from the shadows and just disintegrate whatever.
The Emperor's Thunder are from an unknown founding and origin. Their 4th Company Captain Hercules Leonidas led a Task Force of the chapter in the in The Fall of Medusa V. They fought in Battle Zone Edethor, in which they destroyed the Tyranids infesting the Labyrinth war zone. The Task Force defended the Mortise Line war zone from the Xenos. The 4th Company was later one of the forces that fought to cleanse the Sybilla Mines. However, the mines were claimed by the forces of Chaos, in the end.
I imagine they use iron rain tactics giving the impression of thunder when they land. Also uses the big guns like Heavy Bolters and Plasma Cannons, to help reinforce the sound of encroaching thunder. Visually they could be reminiscent of Norse iconography like the SW, but more imperial, and less wolfy.
The Omega Marines are from an unknown founding (presumed 26th, as they were founding in M40), but unknown heritage. They committed their entire chapter (about 9 companies worth of marines) to the 3rd War for Armageddon. Their most notable deed was to send 9 Dreadnaughts, led by Weyland, to support 8 Dreadnaughts of the Angels Porphyr at Gate IX against various Killa-Kans and Deff Dreads. This was considered the largest recorded instance of Dreadnought vs. Dreadnought combat. Granted the scribes apparently forgot about most Horus Heresy battles.
This chapter is weird in the fact that despite their early appearance, many never heard of these guys until they appeared as one of the free chapters in the class customizer in SM2. I never heard of these guys, but they seem cool.
The Brotherhood of the Bear are from an unknown founding and origin. They were created by Oysten Berg a former GW employee. They were another one of the chapters created for the N. Europe WD's Chapter Master Competition and was featured in WD 298 (UK).
While the obvious is a very unique successor of Space Wolves, however boring. So idk, just not SW.
The Knights Indulgence are a chaos warband who worships the Chaos God Slaanesh. However this has not been the case for very long. Before the warband fell they were known as the Champions of Dedication, a chapter built on the principle that the Emperor was the only god. These Marines were what the Imperium considered the gold standard of what a chapter should be; reliable, zealous, and most importantly self-disciplined. Rarely did they give into their own desires, this is what would launch them into Slaanesh's grace.
In 759.M40, the Chapter's 6th Company was sent to eliminate a rebellion on the world of Benorat II. As the Champions were on their way to the world, they were caught in a warp storm. In 809.M40, the company re-emerged, significantly depleted. The ‘stranded’ as they were called, returned to their homeworld of Extasos. Upon their arrival they were met with the Chapter Master, High Chaplain, and an Inquisitor from the Ordo Hereticus. The Inquisitor wanted to conduct some purity test, which all came back negative for corruption.
However the marines that returned were exhibiting weird behaviors. They began adding runic markings to their grey, unadorned armor, after seeing visions from the “Emperor”. These runes, to the knowledge of none were sigils of Slaanesh. The 6th's Captain Garon Deseri, had prayed to the “Emperor” to get him and his company out of the warp, in exchange for something never listed. After the company returned many who knew him noticed that he had to experience significant lapses in determination, as if he had better things to do. Before long Deseri had roughly half of the Chapter wearing the sigils and which had begun making individuals act on their own wants. Which included adding garish details and colors, overly ornate designs, and actively ignoring the codex. He said that the “Emperor” had sent him a vision saying that any who mark their armor with the sigils will be saved when the time comes, by his angels.
12 years later, the Inquisitor who had conducted the tests, returned to do a follow-up, only to find the chapter had rebelled and was in the midst of a Civil War. The Inquisitor requisitioned a passing army to assist the loyalists led by the Chapter Master. The Loyalist marines and the Inquisitor's force managed to push the Traitors back to their command base, due to Deseri's lapses in determination. In an act of calculated risk or abject disregard, Deseri ordered the Librarians under his thrall to unleash as much psychic power as they could at the enemy force. By doing this act, they managed to open a substantial tear in reality, which sent forth the ‘Angels’. What actually flooded though the Rift was a force of Slaanesh demons. The demons along with the remaining renegades killed most of the Loyalists and pushed the rest off Extasos. As the cost of opening the tear on the planet was subsequently sucked into the warp and lost. With their victory Deseri and his remaining followers renamed themselves to the ‘Knights Indulgence’ and have since scourged the galaxy, as many in the warband conduct war the way they want. Some with close-range assaults or by letting mortals and warp-spawn do it for them.
Deseri had never been wrong about his statement, he just never put in the details. He knows he gave up to get out, as no one comes out the same as they entered. What we do know is he didn't give up his guilt, as he regrets his actions to this day.
The Angels of Redemption (AoR) are an Dark Angels successor of the prestigious 2nd founding. Although they are almost as famous as their parent chapter, though they are known to ditch allies to hunt Fallen. They have even earned the fury of other chapters, who have called for their censure, thought this has been delayed due to the Great Rift. The Great Rift has helped AoR to continue their hunts. The AoR differ somewhat from their parent chapter. They which replaced the 1st and 2nd Companies with the Deathwing and Ravenwing respectively. Instead, the AoR have dubbed the first two companies as the Redwings.
They have fought in various wars which includes but are not limited to: Forgotten Wars, Cataclysm of Souls, Gothic War, Defense of Gatlinghive, Achilus Crusade, 3rd War of Armageddon, Battle of the Caliban System, 13th Black Crusade. That was all before the Great Rift. Invasion of the Stygius Sector, War of Beasts committing 1 Company is sent as part of the Unforgiven force, Nachmund Rift War, Arks of Omen Campaign specifically the Battle of Idolatros. Those were after the Great Rift.
The Raven Covenant are from an unknown founding and origin 🤨. Their only documented conflict was The Relief of Harleycrypt Tertius, during the Prosperan Rift War. In which the Chapter commied 5 Demi-Companies. (~250 Marines)
I like to think they are chimeric in nature; a mix of 1k sons and RG. Their Librarians could have a much more substantial role in the Chapter, they could be more influential then the Captains. Perhaps it could be close to what the Blood Ravens did, in which the Chapter had the possibility for the Chief Librarian to also be the Chapter Master at the same time.
The Black Hawks are from an unknown founding and origin. Although, they have no lore, its the heraldry is where they are at. A Hawk's shoulder pads indicate what squad they belong to: black: Tactical Squad, red: Devastator Squad and white: veterans (including Terminators and Sergeants). Avian symbolism is prevalent the Chapter; most Black Hawks wear MKVI 'Beakie' helmets and powerpacks with bird details.
While I know this is going to sound bland, but I think they are a Raven Guard successor. I think they could operate like U.S. Rangers. The reason for their unique role marking could be a result of a prior incident where the 5th Company (or something) had their ships dropped from the sky, which screwed up their vox and they needed an easier way to know what role each marine was.