I've been working on this piecemeal for a while now. There's a few different ideas in this post - a system for mental damage that's more focused on mechanical penalties than roleplaying penalties, a class that acts like a Thief or Ranger jack-of-all-trades but for the weird and supernatural, a summoning table inspired heavily by Lamentations of the Flame Princess... look upon my works, ye mighty, and save vs. despair.
Stress and Trauma
Whenever you fail an Intelligence, Wisdom, or Charisma save, gain 1 Stress. You might gain more, depending on the effect.
Whenever you gain Stress, roll d20+WIS. If you roll equal to or under your stress, you Crack. Roll d6 to see how. Each time you Crack, step up the die size for the next time you roll.
Cracking (d6 → d8 → d10 → d12 → d20)
1-2. Panic. +d6 Stress (don’t roll to Crack, though).
3. Twitchy. Disadvantage on Dexterity rolls.
4. Phobia. Gain 1 stress when you encounter something that reminds you of this stressor.
5. Fight-or-flight. Save vs. fleeing. If you succeed, you need to attack the stressor at least once.
6. Deadened. Lose your powers of (d4): 1. Sight, 2. Hearing, 3. Touch, 4. Speech.
7. Hallucinations. If you look for or listen to stuff, the GM might describe something different. Disadvantage on Wisdom and Charisma saves.
8. Rage. You enter a Rage as Barbarian. You can’t end it without taking damage.
9. Paranoia. No one counts as allies to you; must save to accept aid or work in team.
10. Amnesia. Lose all abilities associated with your most recent level.
11. Breakdown. You must Save to do anything.
12+. Catatonic. Remove your character from the session until healed. You can bring in another character or play a hireling.
On a short rest, remove d4 Stress. On a daily rest, remove d12 Stress, and remove a Cracking result of 6 or less. On a long rest, Stress resets to 0, and remove a Cracking result of 12 or less.
The truth is out there.
Occultist 1: Eccentric Trinkets, Weirding Way of choice, random Weirding Way
Occultist 2: Second Sight, +1 random Weirding Way
Occultist 3: Summoning Circles, +1 random Weirding Way
Occultist 4: Esoteric Ascension, +1 random Weirding Way
Eccentric Trinkets: Your pockets contain multitudes. On a [Occultist level]-in-6 you can find a strange item on your person that will give you advantage in a very specific relevant situation (can't try more than once for the same situation). You can keep [level] of these items on you; you have to discard old ones to find new ones.
1. Random spell as Wizard (+1 die per 5 stress on Ascension)
2. Random miracle and domain as Cleric (+1 die per 5 stress on Ascension)
3. Random field as Scholar (+1 chance-in-6 on Ascension)
4. Random cut as Butcher (can make an additional cut of that type from a butchered creature per 5 stress on Ascension)
5. Speak with [something] (d6: 1. animals, 2. plants, 3. items, 4. zeitgeist, 5. magic, 6. corpses), works for d3 questions or until you bother it (additional question per 5 stress on Ascension)
6. Induce emotions by voice, targets get saves vs. strong/dangerous emotions (targets have disadvantage at 6 stress on Ascension)
7. Extra sense within 30' (d6: 1. tremorsense, 2. infravision, 3. lies, 4. danger, 5. treasure, 6. heartbeats) (+30' and +1 sense per 5 stress on Ascension)
8. Prophetic dreams each night on 1-in-6 (+1-in-6 per 5 stress on Ascension)
9. Constant aura within 30' of (d6: 1. darkness, 2. fear, 3. forgettability, 4. blazing heat, 5. frigid cold, 6. naivete) (+30' and +1 aura per 5 stress on Ascension)
10. Contact a specific extraplanar being (d6: 1. angel, 2. devil, 3. old one, 4. ancestor spirits, 5. djinn, 6. fey), takes 1 hour to get ahold of them, they'll give you information if it's not too much trouble (+1 contact per 5 stress on Ascension)
11. Can convince people of supernatural explanations as Thief's Con Artist (increase duration as Thief levels per 5 stress on Ascension)
12. Telepathy within 30' (+30' per 5 stress on Ascension)
13. Telekinesis on small objects within 30' (+30' per 5 stress on Ascension)
14. You know the True Name of and can summon a random 1HD outsider (as Summoning Circles). (+1HD per 5 stress on Ascension)
15. Can alleviate or cause specific ailment (d6: 1. Diseases, 2. Curses, 3. Mutations, 4. Decay, 5. Stress, 6. a Bad Reputation) on a [Occultist level]-in-6. If you fail, you can't try again.
16. Can become partially intangible. Can do this as a reaction on a [Occultist level]-in-6. (fully intangible, +1-in-6 per 5 stress on Ascension)
17. Random positive mutation. (+1 temporary positive mutation per 5 stress on Ascension)
18. [Occultist level]-in-6 chance for magical effects to backfire or be negated when they target you (whichever is better for you). (+1-in-6 per 5 stress on Ascension)
19. Can reverse effects of age/wear/damage on small items (up to a week). (up to a month/year/any time OR medium/large/giant items per 5 stress on Ascension)
20. Don't need to (d6: 1. eat, 2. breathe, 3. drink, 4. sleep, 5. have blood inside your body, 6. tire from strenuous activity). (+1 need per 5 stress on Ascension)
Second Sight: You can screw up your eyes, which turn strange and wild, and let you see the Weird that obscures itself to mortals. This includes (but is not limited to) auras, magic, spirits, outsiders, invisible things, and supernatural effects. You can twist your tongue into inhuman geometries, and speak to supernatural forces in their own tongue, even if their minds are irreconcilably strange. You can smudge your hands across the dimensions, and instinctively manipulate the creations of intelligences vast and cool and unsympathetic. These effects last for [level] minutes. Whenever you activate your Sight, gain 1d6 Stress.
Summoning Circles: You can draw a summoning circle to summon an outsider from the veil that shrouds the worlds. This takes 1 hour per HD of the creature, and you can't summon a creature with more HD than twice your level. When you summon it, make an Intelligence test vs. 10+the summon's HD to bind it. If you succeed, it is bound, and you can give it a number of commands equal to the difference between your roll and the target number divided by the summon's HD (minimum 1), for a number of hours equal to the amount you succeeded by. It will follow the letter of your commands, unless they align with its agenda, in which case it will follow the spirit. With a creature's true name, you can summon and bind it reliably, and it is bound for a duration of hours rather than days. If you tie or fail, consult the Disrupted Summons table, use whichever result you failed by.
1-2: Summon will only do things if they directly help its agenda, will obstruct you from defying its agenda
3-4: Summon is beholden to someone other than the summoner, picks random person within HD*1000' to control it
5-6: Must trade favors of equal value with summon in order to command it, otherwise it does what it wants
7-8: Summon breaks free, instantly uses its power as much as possible, then explodes for HD [substance] damage to all onlookers (save for half).
9-10: Summon breaks free, is hostile, wants something from you and will threaten you for its services
11+: Summon breaks free, is hostile, wants to return to the comfort of the void at all costs and punish you for your transgressions.
A summons has a Form, a Substance, a Prominent Feature, a Power, and an Agenda. Its base AC is 0 (or 10 if that's how your system works), and all its stats are 10. It has a default melee attack for d6 bludgeoning damage. All summoned creatures are weak to one of (d6: 1. cold iron, 2. silver, 3. holiness, 4. surprise, 5. magic, 6. fire)
With a number of unique symbolically important items equal to the summon's HD, you can choose one of its traits, or add an additional random trait from a table of your choice. Items used this way are consumed.
1. Humanoid (roll an additional Prominent Feature, +2 DEX, +2 CHA)
2. Canine (powerful sense of smell, +2 STR, +4 CHA)
3. Feline (darkvision, +2 DEX, +2 INT, +2 CHA)
4. Ursine (d8 slashing damage attack, +3 STR, +3 CON)
5. Reptilian (healed in sunlight, +2 AC, +4 CON, +2 CHA)
6. Amphibian (can swim, long tongue grapple attack, +2 CON, +4 WIS)
7. Avian (can fly, +4 INT, +2 CHA)
8. Arachnoid (can spin webs of its substance, climb sheer surfaces, +4 DEX, +2 INT)
9. Insectoid (4-in-6 chance of having flight, +2 STR, +2 CON, +2 DEX)
10. Cephalopoid (can swim, can hover, has tentacle grapple, can camouflage, +2 WIS, +2 INT)
11. Sphere (hovers, telekinesis within HD*10', +2 STR, +2 CON, +2 DEX, +2 WIS, +2 INT, +2 CHA)
12. Unformed Mass (+4 to each of two random ability scores)
13. Tree (immobile, +4 CON, +4 WIS, +4 INT)
14. Weapon (is a random weapon, can be wielded or wield itself, hovers, +4 DEX, +2 CHA)
15. Obelisk (can hover, +2 AC, +4 CON, +2 WIS)
16. Cloud (can hover, resist physical damage, +4 CON, +2 DEX)
17. Crustacean (can swim, +4 AC, +2 STR, +4 CON)
18. Shark (d8 piercing bite attack, target saves vs. bleed, can hover, can swim)
19. Draconid (can fly, +4 AC, +2 STR, +4 CHA)
20. Roll two, its form shifts between them
1. Flesh (roll HD with advantage)
2. Wood (resist bludgeoning, healed by water, weak to fire)
3. Bones (healed by necrotic, weak to bludgeoning)
4. Leaves (can shrink or grow HD sizes, healed by light, weak to fire)
5. Lightning (resist physical damage, move at 10x speed, attacks deal lightning damage, minimum HP)
6. Crystal (resist elemental damage, weak to bludgeoning, invisible 50% of the time)
7. Dreams (immune to physical and elemental damage, only exists in minds of viewers, attacks deal Stress damage, must be fought with psychic damage or other mental effects, can save to disbelieve)
8. Ooze (can squeeze through gaps 1cm wide, healed by acid, weak to slashing)
9. Blood (can squeeze through gaps 1cm wide, resist physical damage, weak to fire)
10. Iron (resist physical damage, melted by fire and acid damage, when liquid can be shaped into new forms)
11. Shadow (immune to all physical damage, resist elemental damage, takes damage from light sources, can teleport between shadows in line of sight)
12. Smoke (resist physical damage, weak to elemental damage, can float and move through spaces, fit into small gaps, anyone engulfed is blinded and saves vs. choking)
13. Fire (deals d6 fire damage to anyone who touches it, resist physical damage, healed by fire damage, weak to water)
14. Water (can squeeze through gaps as a liquid, immune to fire damage, resist physical damage, weak to lightning damage)
15. Stone (resist physical damage, weak to acid, move at half speed)
16. Wind (move at 3x speed, can fly, resist physical damage, weak to elemental damage)
17. Clockwork (resist slashing damage, weak to bludgeoning damage, will perform an additional command)
18. Paper (can deal d6 slashing damage to enemies who touch it, weak to slashing and fire, can fold self to fit into tiny spaces)
19. Radiance (resist physical damage, healed by fire/lightning, those who look upon it save vs. blinding)
20. Roll two, it's made of both
1. Too Many/Too Much (duplicate noun effect)
2. Malformed (negate noun effect)
3. Writhing (+2 DEX)
4. Bladed (d6 slashing damage melee attack OR step up noun attack damage die, change damage to slashing)
5. Enormous (+2 STR, enhance noun effect)
6. Rotting (-2 CON)
7. Beautiful (+4 CHA)
8. Glittering (+2 CHA, can change color)
9. Decorative (-2 STR, +2 CHA)
10. Shifting (becomes a new Noun on use)
11. Dripping (leaves trail of Grease)
12. Furred (+1 AC, resist cold)
13. Mechanical (+1 STR, +1 INT, magnetic)
14. Feathered (+1 DEX, fall slowly)
15. Scaled (+2 CON, +1 AC)
16. See-through (+2 INT, +2 WIS -2 CHA)
17. Spined (d6 piercing damage melee attack OR step up noun attack damage die, change damage to piercing)
18. Hardened (+2 AC)
19. Protruding (functions as additional manipulator limb, d6 bludgeoning damage melee attack OR step up noun attack damage die, change damage to bludgeoning)
20. Roll two, it's both
1. Eyes (can't be surprised, +2 WIS)
2. Maw (d8 piercing damage melee attack)
3. Tentacles (can grapple for free, +2 STR)
4. Tail (d8 bludgeoning damage melee attack)
5. Fangs (d8 piercing damage melee attack)
6. Arms (+3 STR)
7. Legs (+1 STR, double move speed)
8. Wings (can fly)
9. Claws (d8 slashing damage melee attack)
10. Shell (+2 AC)
11. Chains (d8 bludgeoning damage ranged attack, target saves vs. grapple)
12. Robes (+1 AC, looks fancy)
13. Horns (d8 piercing damage melee attack)
14. Bones (resistance to bludgeoning damage)
15. Skin (+2 CON)
16. Hair (+1 AC, +1 CON)
17. Hands (+2 DEX, can grapple for free)
18. Armor (+2 AC, can be taken off)
19. Weapon (roll a random weapon it's wielding)
20. Roll again, and roll an additional Feature.
1. Random spell, HD casts
2. Random miracle, HD casts
3. Invisibility, HD casts
4. Immune to (d6: 1. physical, 2. fire, 3. acid, 4. poison, 5. necrotic, 6. psychic) damage
5. Polymorph self, HD casts
6. Control (d8: 1. fire, 2. water, 3. earth, 4. air, 5. animals, 6. plants, 7. metal, 8. light) within HD*10'
7. Telepathy within HD*10', can attack within range for d8 psychic damage
8. Summon weapons and armor can have HD weapons and armor summoned at once
9. Paralyzing gaze, save negates
10. Anti-magic aura within HD*10'
11. Summon duplicate, halve HD of self and duplicate, HD casts
12. Polymorph other, save negates, HD casts
13. Raise dead as HD1 zombie, HD casts
14. Ability score drain for HD points, save negates (d6: 1. STR, 2. DEX, 3. CON, 4. INT, 5. WIS, 6. CHA)
15. Teleport within HD*50', HD times
16. Always acts first in combat
17. HD/2 levels in random character class
19. Heal as cleric miracle
20. Roll two, it has both
1. To destroy
2. To create
3. To protect
4. To reproduce
5. To consume
6. To accumulate
7. To conquer
8. To sacrifice
9. To seek out
10. To manipulate
11. To survive
12. To enjoy itself
13. To profit
14. To love
15. To serve
16. To die
17. To make friends
18. To escape
19. To deceive
20. Roll two, it wants both
Esoteric Ascension: The more Stress you have, the more powerful your Weirding Ways become. Every 5 Stress you have upgrades your Weirding Ways. Upgrades detailed next to Way.
Occultist 1: Cloak, book of esoteric symbols, quill, ink, diary half-filled with ramblings, engraved knife
Occultist 2: Set of spyglasses and magnifying glasses, chalk, book of supernatural creatures and occurrences (1-in-6 chance to find relevant information, 1-in-6 chance to find incorrect information, GM secretly picks which number is which when you roll)
Skills (d3): 1. Scribe, 2. Archeologist, 3. Noble