Okay, I wanted to wait for feedback before I started, but since my threads tend to get skipped over a lot, I felt I should go ahead and post something for folks to chew over.
Incidentally, yes, I do want to tackle spells, magic items, new weapons, backgrounds, diseases, monsters, feats and the like at some point, but currently my focus is on races and subclasses because, well, those are not only the easiest areas to homebrew in, they're also the ones I most clearly have ideas for.
To start things off, let's talk about the Caliban. Introduced in Swords & Sorcery's update of the Ravenloft setting for D&D 3rd edition, Calibans are magic-spawned, curse-created mutants, individuals tainted in all manner of horrific ways to represent the sins of their ancestry or the ill-fortune of being born or conceived in places that were spiritually polluted. This was a Gothic Fantasy reskinning of the Half-Orc, but mechanically, they weren't very interesting - they were, literally, the 3e Half-Orc with different fluff. So, a fan took it upon himself to rectify this, creating an article for issue #8 of the "Quoth The Raven" net-zine in which a mechanically new form of Caliban was introduced, along with five specific subraces.
Now, the Caliban works wonders for a fantasy style post-apocalyptic world, as it melds excellently with the concept of mutant freaks that goes hand in hand with such settings. Unfortunately, the current "Unofficial Ravenloft 5e Update" over on the Fraternity of the Shadows, for whatever reason, decided to make it's Calibans be divisible into subraces based on territory of origin, rather than using the perfectly good Banshee/Beast/Brute/Cannibal/Witchspawn split they already had. So, that leaves me trying to make them work on their own, and for that, I'm going to need your help.
If necessary, I can and will post all fluff and crunch details relating to the race as it appeared in 3.5, but as Quoth The Raven #8 is still online and can be downloaded for free at the Fraternity of Shadows website, I'd rather not risk copyright entanglement without pointing you all to go there first.
Caliban Racial Core:
Size:Medium
Speed:30 feet
Darkvision60 feet
Freakish Horror:A Caliban automatically has Proficiency in Charisma (Intimidation) checks.
Unnatural Blood:A Caliban belongs to one of the five subraces; Banshee, Bestial, Brute, Cannibal or Witchspawn. Acquire the additional abilities determined by one subrace.
Banshee Subrace:
Ability Score Modifiers:+2 Charisma, +1 Intelligence
Cold Blooded:Existing with the chill in the grave racing through their blood, Banshees are hardly touched by mundane cold. A Banshee Caliban has Resistance to Cold.
Deathly Pallor:You have disadvantage on saving throws to resist diseases and poisons.
Ghostly Keening:As an action, you can cause each creature in a 10-foot radius sphere originating from you to make a Wisdom saving throw. The DC for this saving throw equals 8 + your Charisma modifier + your proficiency bonus. A creature takes 1d6 psychic damage and 1d6 thunder damage on a failed save and are frightened by you until the end of your next turn. On a successful save, a creature takes half as much damage and is not frightened. The psychic and thunder damage increases to 2d6 at 6th level, 3d6 at 11th level, and 4d6 at 16th level. Once you use this feature, you can't use it again until you finish a long rest.
Bestial Subrace:
Ability Score Modifiers:+2 Strength, +1 Wisdom
Feral Instincts: A Beast suffers Disadvantage on Intelligence checks.
Hide of the Beast: A Beast Caliban’s unarmored AC is 11 + Dexterity modifier.
Natural Weapons: A Beast always has some uniquely useful offensive mutation. At character creation, choose one option for modifying your Unarmed Strike damage: inflict Slashing damage, inflict Piercing damage, or boost Bludgeoning damage to a base of 1d4 points. This choice cannot be changed later.
Run With The Pack: A Beast invariably has some mutation that increases its mobility in some way. Choose one of the options below to determine your specific bonus: you cannot alter this selection afterwards.
Loping Fiend: Your base walking speed increases to 35 feet.
Treetop Scrambler:You gain a Climb speed of 20 feet and have Advantage on Strength (Athletics) and Dexterity (Acrobatics) checks. Your base walking speed decreases to 25 feet.
Horror from the Deep:You gain a Swim speed of 30 feet and the Amphibious trait, allowing you to breathe both water and air. Your base walking speed decreases to 20 feet.
Winged Abomination:You gain a Fly speed of 20 feet and suffer Vulnerability to Bludgeoning damage.
Brute Subrace:
Ability Score Modifiers:+2 Strength, +1 Constitution
Powerful Build:A Brute counts as one size larger when determining its carrying capacity and the weight it can push, drag, or lift.
Juggernaut:A Brute counts its Strength as +2 higher for dealing damage with Unarmed Strikes, and can add its Proficiency bonus to Strength checks made to break objects.
Savage Grapple:When a Brute successfully grapples an opponent, it can deal damage as though it had made an unarmed strike. Additionally, if it begins its turn grappling an opponent, it has advantage on rolls to attack its grappled opponent with an unarmed strike.
Hot-Blooded:A Brute suffers Disadvantage on saves to avoid having its emotions manipulated.
Cannibal Subrace:
Ability Score Modifiers:+2 Dexterity, +1 Constitution
Eater of Vile Things:Cannibals possess Resistance (Poison) and are immune to non-magical diseases. A Cannibal can still become infected with a disease for purposes of carrying it and spreading it to other creatures.
It Will Not Die:A Cannibal passes Death Saving Throws on a 5 or higher, instead of a 10 or higher. It also has Advantage on saving throws made to avoid being rendered Unconscious.
Graveworm:Cannibals possess a Climb speed of 20 feet, can Squeeze through spaces sized for a creature two size categories smaller than they are, suffer no penalties for squeezing through a space sized for a creature one size category smaller than they are, and may crawl at their normal speed.
Witchspawn Subrace:
Ability Score Modifiers:+2 Intelligence, +1 Charisma
Hexcrafter: A Witchspawn knows three spells of its choice taken from the Warlock spell list. A cantrip at first level, a 1st level spell at third level, and a 2nd level spell at fifth level. A Witchspawn's racial spells use Intelligence as a casting trait and cast at their default level. A witchspawn's racial cantrip may be used at will. Its racial 1st and 2nd level spells may each be cast once per long rest.
Blood Magic: A Witchspawn may sacrifice hit dice when casting a spell through its Hexcrafter trait to increase its effectiveness as if the witchspawn had increased the spell's slot. Each hit dice sacrificed increases the effective spell slot of the Hexcrafter spell by 1 level.
Spell-Seared Flesh: A Witchspawn is treated as being one size smaller for determining its carrying, pushing and pulling capacity. It also suffers Disadvantage on Constitution checks.