I started work on this yesterday, but I ended up giving it a lot more thought than I thought I was. So here's my attempt, using a real Lovecraftian god
I know the level 5 is kind of interaction heavy as well, but the Darkvision, seeing through illusions, and seeing invisible creatures can very much benefit exploration and combat.
Let me know what you think! Eldritch Pact:
Nyarlathotep, The Chaos that Crawls
You have found ancient tomes and scoured long forgotten ruins seeking the long lost spells and incantations needed to contact an Elder Being. After years of research, you have finally amassed enough information to conduct a ritual to contact Nyarlathotep, the Black Man, the Chaos that Crawls. Being an entity of bargaining, Nyarlathotep agrees to offer you power, in exchange for your devotion. The Warlock will work, in secret, towards the ends of Nyarlathotep. The DM decides what his motives are, but they are generally nefarious and foul. Also, what you don't know is his hidden price, your Sanity.Sanity
: Nyarlathotep is an alien being and the human psyche can not withstand him for long, much less channel his powers. Thus as you gain greater and greater abilities, you lose a part of what makes you human, and come closer and closer to a slave of the Crawling Chaos.
Benefit: You character begins the game with 10 sanity. Each pact ability you learn drops this sanity score by 1. Each time you use one of your pact abilities, you must roll an intellegence or charisma save, DC 15, adding your sanity to the save. Making this save is easy at first, but becomes harder and harder as you progress. If the save is passed, the pact favour goes off as normal. If the save is failed the pact goes off as normal, but you glimpse a bit of forbidden knowlege or power, that temporarilly drives you off the deep end. Roll a d10 and recieve it's effect starting on your next turn. No matter what you roll, however, the player will not forget his pact, nor how to use his Warlock abilities. Other class abilities may be temporarilly forgetten however. Multiple effects can stack, and you can gain multiple of the same affliction (eg. forget about 2 different things with selective amnesia).
1. Obsession - For the rest of the day you become completely fixated on a person, idea, or object of the DMs choice. The Warlock will attempt to protect it, horde it, and be with it at all costs.
2. Mania - The Warlock will attempt to attack anything around it full force. For 1d4 rounds, the warlock will attack the nearest live, or seemingly live, target to him.
3. Delusion - For the rest of the day the Warlock wholly believes something that is not true. Whether it's that he's the King of these lands, he is a different person, or even that Elves don't exist. Effect is up to the DM.
4. Paranoia - The Warlock becomes fiercly paranoid for the rest of the day. Everything and everyone might be out to get him and plotting behind his back.
5. Phobia - For the rest of the day the Warlock developes an irrational phobia of a subject chosen by the DM. The Warlock will do whatever it takes to avoid the subject of his fears, and if he cannot get away he will freeze in terror. The fear does not have to be something present at the time, but it's usually far more humorous if it is.
6. Babbling - The Warlock spends his next turn babbling incoherently in a language no one understands. He is considered stunned until the end of his next turn.
7. Selective Amnesia - The Warlock forgets something, or somethings, that he once knew, decided by the DM. He might forget his name, his traveling companions, or even what their mission is.
8. Voices - For the rest of the day the Warlock will hear voices, whispers in his mind that no one else can hear. They might command him to do unspeakable things, they might try and uproot his trust in his allies, or they might plain insult him. The intent of the whispers is up to the DM.
9. Shaken - The Warlock has looked into the eyes of terror, and it has shaken him to his bones. For the rest of the day, the Warlock has disadvantage on Wisdom saves.
10. Channel Power - You have temporarilly tapped into a great power beyond your wildest dreams, increasing the power of your next attack. Your next attack deals an extra 2d6 damage. However, immediately after the attack, the Warlock must make another Intellience saving throw for Sanity, as if he had used a pact favour.
Upon reaching 4 sanity, you gain advantage on all saves to avoid madness or confusion, since you have already faced these head on. Upon reaching 0 sanity, you are considered insane, but do not have the madness effect applied at all times. You are a complete tool for Nyarlathotep to use, and will do his bidding no matter what. You are also immune to all effects that cause madness or confusion.Level 1
: Through your devotion to Nyarlathotep you have gained a small inkling of his powers. He is the messenger of the gods, and thus he has granted you limited telepathy. However, your sanity begins to drain.
Benefit: You may expend a pact favour to be able to converse telepathically for the next hour. This is a one way comminication though. You can talk to your allies telepathically, but they cannot talk back to you without their voice. As well, you may expend the pact boon to read the surace thoughts of a person for 1 round. They can make a wisdom saving throw, DC 10+Warlocks int modifier, to negate the effect.Level 3
: Your service to Nyarlathotep has not gone unnoticed. For your continued obedience, he grants your an ability to help protect you from would be assailants that might try and end your work. You can grant the attacker a look into the eyes of the Crawling Chaos, causing him to break. However, your wall of sanity is starting to crack.
Benefit: As a reaction you can force the attacker to glimpse the madness that is Nyarlathotep. The attack must make a Wisdom saving throw, or else become stunned until the beginning of their next turn. This does interrupt the attack. Creatures without sight of any kind are uneffected by this ability. When the ability is used, your eyes become completely black, like voids leading into the darkness.Level 5
: Your ongoing servitude has granted you another nibblet of power from your Lord. This time he offers you sight into the truth of the world, past the thin veil that protects the human Psyche. However, with this new perspective, more and more of your Sanity is falling through your fingers.
Benefit: As an action you can invoke this favour. For 1 minute you gain darkvision (60 ft.), as well as advantage on saves and checks to see through illusions, disguises, and lies. You can also see invisible creatures. While this ability is active, people might notice your irises seem to pulse, dialate, or even change color randomly.