Ideas for "Curse of Nihilism" Item in 5E Campaign

[Zozma]

I'm running the module/mini-campaign Deep Carbon Observatory, which has themes of, among other things, forbidden knowledge and looking too far. At one point in the mega-dungeon the players can run across a library filled with ominously titled texts in an even more ominous format. They're mostly treated as flavor in the campaign, but I decided to make the library into a pseudo Deck of Many Things, with each book having the potential to permanently alter the reader in positive and negative ways. Each book is meant to have at least one positive effect and one negative effect, but the good aren't necessarily meant to outweigh the bad, or vice versa, and some effects may be entirely situational.

One of these "cards" that I've been having a hard time coming up with effects for is titled "The Futility of Any Possible Deed." I want it to turn the player into the ultimate nihilist, complete with in-game effects that reflect this. Ideally it won't cripple the player or make the game unenjoyable for them, so effects like "roll a saving throw to get out of bed each morning" are out. At the same time, I'm not particularly worried about balance; the library comes at the end of the campaign, and we don't plan on using the characters afterward.

Does anyone have any ideas? For possible reference here are some of the other books I've come up with that I'm feeling pretty comfortable with:

Spoiler: The Futility of Any Possible Deed

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The text would make Nietzsche weep impotent tears. It is an unparalleled treatise on nihilism, complete with data, models, and arguments so watertight that it would make rebuttal fruitless--doubly so.
You feel ennui seeping into your bones and weighing you down as you read. You're sharper for the experience, more aware, but certainly no better off. Purpose is illusion, destiny a lie, and what drives you and everyone is the compulsion to distance oneself from the one truth of the universe: life is meaningless.

-Effect 1?
-Effect 2?

Spoiler: Conversations With Those Below

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The Great Old Ones is a designation for a genus of entities that were born and evolved just beyond the reach of starlight. They were lured to the world like prey to an angler and observed, with their alien senses, the makings of life. Like all living creatures they were instilled with the instinctive compulsion to reproduce, but--owing to their individually unique physiologies--could not find compatible mates among their own kind. They took primitive men and women and birthed surrogates, abominations such as "mind flayers" and "beholders," before the jealous gods of man chased them--children and all--to the darkness below.
-Your mind has figuratively expanded, and is now capable of insights beyond what it was originally capable of. Unfortunately, your mind has also literally expanded; there is a plum-sized growth between your eyes shaped like a head of cauliflower. It distorts your vision and has obvious social consequences.
-Your Intelligence permanently increases by 2, your Charisma decreases by 2, and your Wisdom decreases by 1.

Spoiler: The Grain of Time

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Time has a navigable, malleable structure, and you now understand it more than anyone living. Its intricacies are beyond crude manipulation--the book references machines you don't understand and spells long forgotten--but there are ways to "cheat," to introduce some slack in a taut cord. The process is indescribable, even though it has just been described to you; like flexing a muscle you don't have or picturing a color you've never seen. There is a price to pay, but such is always the case with higher knowledge.
-Once per long rest you may cast haste on yourself as a free action. The effect lasts two turns, after which you are affected by two turns of slow.

Spoiler: How They Come Against You When They Do

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You see your allies with new perspective. They have a subtlety to them that you've never noticed before, a warped intelligence in their eyes. You see patterns that you once mistook for innocuous habits, patterns that belie their hidden intentions. They plot against you, and such is their gall that they do it right in front of you. But you see through them. You're prepared.
-You can never be surprised in combat, and you are immune to sneak attack and assassination damage.
-You cannot sleep in the company of your party--or anyone for that matter. You must put at least one locked or barred door between you and them or make some similarly drastic accommodation, or you simply won't be able to benefit from a long rest.
-You probably don't trust anything anyone says, anything they give you, or any spells they cast on you. In all likelihood you need to either kill or abandon your party members. Ultimately it's up to you to decide how you want to roleplay this turn of events, but at the core of your being is a fundamental and inescapable mistrust of every living, intelligent creature.

Spoiler: Things that Cannot be Found

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The presented information details varieties of subterranean insects and rodents with such excruciating nuance that it would bore the most dogmatic pedant. However, you are able to gleam a fascinating truth from the described survival tactic of one breed of moth: the relativity of space.
Time is relative, of course; anyone who has watched a pot boil knows this. This is a trait it shares with space, though most living things must unlearn this fact early on or risk becoming Lost. Adept magicians rely on magic to travel across warped space while the fey navigate the curves of the world by instinct, but all it takes is a different perspective to see the folds, to walk the horizon like a tightrope. Nothing can remain hidden for overly long to someone with this knowledge, but its possession comes at a cost. If stretched too far space may become permeable, and you will find yourself falling through the void left behind.
-Once per long rest you may choose to automatically succeed on a Perception or Investigation roll. You may do so after you already rolled. Further, you may spend your use of this ability to obtain the key to any conventional lock, regardless of whether or not one actually exists. This ability cannot detect invisible creatures or things otherwise shielded from scrying.
-Whenever you roll a natural 1 on a Stealth check--regardless of whether or not you have advantage or luck--you become Lost and must navigate your way back to the world of Euclidian space. You are essentially under the effect of the Maze spell, and may begin rolling Intelligence checks to escape at the DM's discretion. Expect to escape only after your absence becomes detrimental to the party.

[WrittenInBlood]

You can help yourself with some of those, in any combination:

Negative:
- character always goes last in the initiative order
- character's rolls made during reaction turn have disadvantage
- character can never benefit from Bardic Inspiration dice
- any of character's rolls that score highest possible number must be rerolled

Situational:
- character's ability checks always score 4+ability modifier+proficiency bonus (so 15 at most), without need of rolling (or more random version: for ability checks, use d10 instead of d20)

Positive:
- character is immune to Frightened condition, and Intimidation attempts against her fail automatically (or weaker version: saves vs Frightened have advantage, and Intimidation checks vs character have disadvantage)
- character has +3 bonus to rolls made with disadvantage

Any chance you will post more of those books?

[Bhu]

Which version of nihilism? https://en.wikipedia.org/wiki/Nihilism

[Zozma]

You can help yourself with some of those, in any combination:

Negative:
- character always goes last in the initiative order
- character's rolls made during reaction turn have disadvantage
- character can never benefit from Bardic Inspiration dice
- any of character's rolls that score highest possible number must be rerolled

Situational:
- character's ability checks always score 4+ability modifier+proficiency bonus (so 15 at most), without need of rolling (or more random version: for ability checks, use d10 instead of d20)

Positive:
- character is immune to Frightened condition, and Intimidation attempts against her fail automatically (or weaker version: saves vs Frightened have advantage, and Intimidation checks vs character have disadvantage)
- character has +3 bonus to rolls made with disadvantage

I like these suggestions a lot. I'm thinking a combination of disadvantage on initiative, not being able to benefit from inspiration, advantage on fear saving throws, and possibly an alignment change to true neutral.

Any chance you will post more of those books?

Sure, though I'm not as happy with them.

Spoiler: Those Taken From Above (written on a scroll with radium ink)

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The elves were the first to develop the Ashen Brand. It was stolen from them by the dwarves, who taught it to the gnomes. This was thousands of years ago, when the ancient civilizations were rounding their apex, when those in power could no longer deny the common wisdom that all nations are doomed to fall.
Cults of decadence rose, dedicated to gods whose dogma was excess and whose tribute was blood. Bastards made claims to thrones, generals turned their armies against their banners, and warlocks sealed packs with beasts of fire and shade. When forces rose to quell the dissidence they scattered to the shadows like roaches, breeding new support and biding their time.
The Brand was the remedy. It was a curse, it was a contagion. Traitor and heretic were marked, their skin stained and their hair blanched, and through contact they spread it to family, kin, and comrade. When the curse had reached its height they were gathered, the guilty in deed and by association, and through sorcery banished to the inescapable depths that would be the Underdark.
-You have advantage on all saving throws made against the special attacks of the natural denizens of the Underdark. This includes spell-like abilities, but not spells themselves: you'd have advantage against a beholder's rays or a mind flayer's psionic powers, but not a drow wizard's spells, for example.
-The information itself doesn't hurt you, but being next to the radium for so long was bad for your health. You have radiation poisoning and permenantly lose 1 point of Constitution. To add insult to injury all your hair has fallen out, and you are totally sterile. It may be possible to reverse the damage, but you get the feeling a simple antidote isn't going to do it.

Spoiler: The Addictions of Gods: Narcotics and Vices of the Divine

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There is no transcendence. The beings you called "gods" are as flesh and blood as any mortal, and subject to similar failings. You now know what these weaknesses are, and with this knowledge, a darker revelation: every deity is a pretender to the throne of creation. They feed on the reverence of their worshippers, prolonging their lives and rationing divine magic that should belong to all living things.
-You can no longer worship or pray to any god. You can never take any levels in Cleric, and if you have any cleric levels they must be reassigned.
-You have understanding of the addictions of the gods, from their basic need for worship to their most repugnant of vices. The immediate applications of this knowledge are probably nonexistent; exploiting it would be an adventure in and of itself. However, if you were so inclined, you are in a position to dethrone the gods.

The campaign also gives a few more titles, but I'm not sure if I'll use them: "The Enclosing Nature Of Things", "Life Without Light: Abyssal Crops and their Management", "The Masonry of Shadow: Building With Darkness and Light"

Which version of nihilism?

Existential and possibly moral.

[Bhu]

Moral nihilism will run into issues, as moral nihilists believe any form of morality or ethics are purely artificial constructs, and have no meaning or importance. Possible advantages are you would have a lack of hesitation or inhibitions, and you tend to be more aware of your surroundings. Downsides are stress (you know your stress will disappear if you violently murder the cause of it, but that darn society won't let you) and a reputation for being immoral (or at least amoral among those who understand). Attempts to influence you via social skills would be penalized as the guy giving you a pitch of any kind is unaware that you are not teh sort of audience he is used to and you don't respond similarly. Also your own use of social skills would suffer as you don't quite "get" people who don't think like you, and the kneejerk reaction is to assume they're clueless idiots. Despite this you would likely have a personal sense of right or wrong from your upbringing, which mains you can range from just mildly cynical to openly psychopathic.