Sources:
- Basic Rules (BR), Chapter 3: Classes
- System Reference Document (SRD), p. 8-55
- (Note: D&D Beyond's "Basic Rules" listing is actually an
inclusive combination of the Basic Rules PDF and the SRD)
- Player's Handbook (PHB), Chapter 3: Classes
- Sword Coast Adventurer's Guide (SCAG), Chapter 4: Classes
- Xanathar's Guide to Everything (XGtE), Chapter 1: Character Options
- Tasha's Cauldron of Everything (TCoE), Chapter 1: Character Options
- Van Richten’s Guide to Ravenloft (VRGtR), Chapter 1: Character Creation
- Fizban's Treasury of Dragons (FToD), Chapter 1: Character Creation
- Guildmasters' Guide to Ravnica (GGtR), p. 25-27
- Mythic Odysseys of Theros (MOoT), Chapter 1 > Subclass options
- Wayfinder's Guide to Eberron (WGtE), Appendix D
- Eberron: Rising from the Last War (E:RftLW), p. 54-63
- Explorer's Guide to Wildemount (EGtW), p. 182-186
- Dungeon Master's Guide (DMG), p. 96-97
Artificer (WGtE, E:RftLW, TCoE)
Artificer Specialists:
- Alchemist (WGtE, E:RftLW, TCoE)
- Armorer (TCoE)
- Artillerist (E:RftLW, TCoE)
- Battle Smith (E:RftLW, TCoE)
Barbarian (SRD, PHB)
Primal Paths:
- Path of the Berserker (SRD, PHB)
- Path of the Totem Warrior (PHB, SCAG)
- Path of the Battlerager (SCAG)
- Path of the Ancestral Guardian (XGtE)
- Path of the Storm Herald (XGtE)
- Path of the Zealot (XGtE)
- Path of the Beast (TCoE)
- Path of Wild Magic (TCoE)
Bard (SRD, PHB)
Bard Colleges:
- College of Lore (SRD, PHB)
- College of Valor (PHB)
- College of Glamour (XGtE)
- College of Swords (XGtE)
- College of Whispers (XGtE)
- College of Eloquence (MOoT, TCoE)
- College of Creation (TCoE)
- College of Spirits (VRGtR)
Cleric (BR, SRD, PHB)
Cleric Domains:
- Knowledge Domain (PHB)
- Life Domain (BR, SRD, PHB)
- Light Domain (PHB)
- Nature Domain (PHB)
- Tempest Domain (PHB)
- Trickery Domain (PHB)
- War Domain (PHB)
- Arcana Domain (SCAG)
- Forge Domain (XGtE)
- Grave Domain (XGtE)
- Order Domain (GGtR, TCoE)
- Peace Domain (TCoE)
- Twilight Domain (TCoE)
- Death Domain (DMG)1
Druid (SRD, PHB)
Druid Circles:
- Circle of the Land (SRD, PHB)
- Circle of the Moon (PHB)
- Circle of Dreams (XGtE)
- Circle of the Shepherd (XGtE)
- Circle of Spores (GGtR, TCoE)
- Circle of Stars (TCoE)
- Circle of Wildfire (TCoE)
Fighter (BR, SRD, PHB)
Fighter Archetypes:
- Champion (BR, SRD, PHB)
- Battle Master (PHB)
- Eldritch Knight (PHB)
- Purple Dragon Knight (SCAG)
- Arcane Archer (XGtE)
- Cavalier (XGtE)
- Samurai (XGtE)
- Echo Knight (EGtW)
- Psi Warrior (TCoE)
- Rune Knight (TCoE)
Monk (SRD, PHB)
Monastic Traditions:
- Way of the Open Hand (SRD, PHB)
- Way of Shadow (PHB)
- Way of the Four Elements (PHB)
- Way of the Long Death (SCAG)
- Way of the Sun Soul (SCAG, XGtE)
- Way of the Drunken Master (XGtE)
- Way of the Kensei (XGtE)
- Way of Mercy (TCoE)
- Way of the Astral Self (TCoE)
- Way of the Ascendant Dragon (FToD)
Paladin (SRD, PHB)
Sacred Oaths:
- Oath of Devotion (SRD, PHB)
- Oath of the Ancients (PHB)
- Oath of Vengeance (PHB)
- Oath of the Crown (SCAG)
- Oath of Conquest (XGtE)
- Oath of Redemption (XGtE)
- Oath of Glory (MOoT, TCoE)
- Oath of the Watchers (TCoE)
- Oathbreaker (DMG)1
Ranger (SRD, PHB)
Ranger Archetypes:
- Hunter (SRD, PHB)
- Beast Master (PHB)
- Gloom Stalker (XGtE)
- Horizon Walker (XGtE)
- Monster Slayer (XGtE)
- Fey Wanderer (TCoE)
- Swarmkeeper (TCoE)
- Drakewarden (FToD)
Rogue (BR, SRD, PHB)
Roguish Archetypes:
- Assassin (PHB)
- Thief (BR, SRD, PHB)
- Arcane Trickster (PHB)
- Mastermind (SCAG, XGtE)
- Swashbuckler (SCAG, XGtE)
- Inquisitive (XGtE)
- Scout (XGtE)
- Phantom (TCoE)
- Soulknife (TCoE)
Sorcerer (SRD, PHB)
Sorcerous Origins:
- Draconic Bloodline (SRD, PHB)
- Wild Magic (PHB)
- Storm Sorcerer (SCAG, XGtE)
- Divine Soul (XGtE)
- Shadow Magic (XGtE)
- Aberrant Mind (TCoE)
- Clockwork Soul (TCoE)
Warlock (SRD, PHB)
Otherworldly Patrons:
- The Archfey (PHB)
- The Fiend (SRD, PHB)
- The Great Old One (PHB)
- The Undying (SCAG)
- The Celestial (XGtE)
- The Hexblade (XGtE)
- The Fathomless (TCoE)
- The Genie (TCoE)
- The Undead (VRGtR)
Wizard (BR, SRD, PHB)
Arcane Traditions:
- School of Abjuration (PHB)
- School of Conjuration (PHB)
- School of Divination (PHB)
- School of Enchantment (PHB)
- School of Evocation (BR, SRD, PHB)
- School of Illusion (PHB)
- School of Necromancy (PHB)
- School of Transmutation (PHB)
- Bladesinging (SCAG, TCoE)
- War Magic (XGtE)
- Chronurgy Magic (EGtW)
- Graviturgy Magic (EGtW)
- Order of Scribes (TCoE)
D&D Beyond has a nicely formatted reference for all of the available classes/races/etc. Subclass and subrace information is also available by looking at the parent class or race's details. It should be noted that the free access materials do not include much outside of the D&D Basic Rules. They do offer other books' content, but that content must be purchased separately.
D&D Beyond
Classes Page
Races Page
1 These subclasses are included in the DMG and can be used only with the consent of the DM because they are generally made to be used for NPCs only or only in special DM-granted circumstances. However, the DM may choose to make these subclass options more generally available.
Blood Hunter is unofficial third-party content by Matt Mercer, but he and Critical Role have an advertising partnership with D&D Beyond.
Nothing makes the Blood Hunter class inherently special as compared to any other homebrew class published on DMsGuild or D&D Beyond. It's not any more official or AL-legal than any other homebrew class.
The only reason it has a special placement/presentation on D&D Beyond (DDB) is that Matt Mercer and Critical Role have an advertising partnership with DDB. Apparently, as part of that partnership, DDB has agreed to provide special listings for Mercer's homebrew Blood Hunter class and his Gunslinger fighter subclass. (The same items appear on DMsGuild: Blood Hunter,1 and Gunslinger.)
DDB's character creator also lists "Critical Role Content" separately from other "Homebrew Content", presumably for the same reason.
This changelog on the D&D Beyond forum discusses the partnership:
Critical Role Partnership
We are also very happy to finally share that we have entered a long-term partnership with Critical Role!
As part of the sponsorship, we will be adding some of the custom content used at the table in the show, starting with the blood hunter class by Matt Mercer.
You can also see in the screen capture above that a new Critical Role Content category has been added. To enable CR content for your character, toggle that category "on" and you will see the blood hunter as a new option in the builder. You can also see the blood hunter under the 'Additional > Classes' section in the main navigation and classes page.
We plan to incorporate more Critical Role content over the course of the partnership, so stay tuned for that here. Also, if you aren't already a loyal viewer, now is an excellent time to jump in and experience a brand new campaign with the cast of Critical Role! Check out the first episode here.
A Twitter user also asked about the partnership and the officialness of the Blood Hunter class:
Twitter user: The Blood Hunter is listed as an additional class on D&D Beyond, under official classes, was it made official?
Jeremy Crawford: The only official classes in D&D are in the Player's Handbook. For a new class to become official in the future, it must appear in a D&D book or must be announced as official by the D&D team.
D&D Beyond: The Blood Hunter is actually categorized under 'Additional Classes' everywhere it appears in DDB. It is specifically not under 'Official Classes' and is not considered official.
Matt Mercer: This. :)
In short: it's not official. It's basically "homebrew"/third-party content, just like anyone else's, except DDB has given it a special placement/designation because of their partnership with Critical Role.
This will not change with the release of the Explorer's Guide to Wildemount book in March 2020. Though it is the first official Wizards of the Coast book about Matt Mercer's setting of Exandria (and the continent of Wildemount within it), it doesn't affect the status of any other content by Mercer.
According to the product listing on critrole.com, the book will contain several new official character options, including 3 subclasses (the Echo Knight for fighters, and the Chronurgist and Graviturgist for wizards) and a number of new spells from Mercer's new dunamancy type of magic, among other new content. However, it will not reprint the content Mercer published on DMsGuild or in Green Ronin's Tal'Dorei Campaign Setting, or make that content any more official.
1 Mercer did release an updated/rebalanced version of his Blood Hunter class in January 2020, but the older version is still available as a separate listing on DMsGuild. He also mentions in this Twitter thread that the version on D&D Beyond will be updated as well.)
Best Answer
There are two sets of rules for ship combat, but the ones you link are not both official
The first set of rules we get for ship combat appears in the Unusual Environments section of Chapter 5 of the Dungeon Master's Guide:
The rules here are very sparse and not the most detailed, but include such things as describing the HP and defenses of various ships.
The later addition of the rules from Ghosts of Saltmarsh provide a much needed improvement on these rules for that setting. These rules appear in Appendix A of the book under Ships in Combat:
The D&D 5e SRD
The D&D 5e SRD does not contain any rules about ship combat. I'm not sure what the source of the rules you link are, but I don't recognize them from any official rulebook. You can find the actual D&D 5e SRD on the Wizards of the Coast website.