The death of a Frenchman, if not "the Frenchman" of my notes.
When the Frenchman dies, all who witness his dying breath save or catch the curse.
Spellcasters
The curse lives in a spell slot. It prefers high-level spell slots, but can be persuaded to take a lower-level slot temporarily. You cannot cast the curse, it just lives there.
When another spellcaster witnesses you casting a spell, they must save or catch the curse also. This is how the curse "reproduces". If you are cunning, you may be able to coax the curse onto a scroll, or convince it to allow itself to be "cast" into another host (without leaving a copy behind). It knows that the target will get a save in both of these cases, so it needs to be a good deal.
When you die, the curse dies with you.
Others
The curse cannot "reproduce" properly if you can't cast spells, so instead it seeks out spellcasters. Intermediate hosts have disadvantage on saves vs. magic, and their skin is covered in crawling tattoos that are offensive, enraging, insulting, confusing, distracting, and profane. Fortunately, these tattoos are only visible to Read Magic, True Seeing, or those with second sight.
"The Op Tattoo", Robert Williams, 1993 (not public domain or anything like that)
On a 1-in-6, the intermediate host has some innate magical potential, and instead carries the curse asymptomatically.
When
you die, the curse will pass into all who witness your death. If you
manage to otherwise rid yourself of the curse, it will leave behind an empty spell slot.
These spells are meant for a nautical LotFP campaign. I haven't tested any of them yet, but I'll let you know how it goes if I do. They're intended to use the draft rules for risky casting.
Drown
Magic User 1
Duration: 2 rounds/level
Rage: Touch
Special: Must have unwillingly taken drowning damage to learn this spell.
Trick a brain into drowning. Each round that the target fails a save (paralyzation), choose to either advance the spell a stage or return to 0th stage. The 0th degree takes effect immediately. Stage 0: Target cannot move, but can speak and breathe. Further saves at a disadvantage. Stage 1: Additionally, target cannot breathe and takes 1d6 subdual damage this round. Stage 2: Additionally, target takes 1d6 (normal) damage. Stage 3+: Additionally, target loses one point from a random ability score (permanent).
If subdual damage + real damage > HP, the target is unconscious and the spell ends. The target must be physiologically able to drown.
Miscasts
Also trick your own brain. The spell affects you the same as the target (use target’s saves for progression).
Trick everyone’s brain. The spell affects everyone around you in a 120’ radius (use target’s saves for progression).
PTSD. Must save or flee from water. Rerolls mean save is at progressive penalty.
Water elemental that loves drowning people is jealous, attacks you (1 HD/level).
Casting this spell is always risky. Reroll frees the caster from this result, as they become hardened to its effects.
Target is immune to the spell, and can now hold their breath twice as long as usual. Caster grows to irrationally hate them if they don’t already.
Gills
Magic User 1
Duration: 6 Turns/level
Range: Touch
As Water Breathing, except lose ability to breathe air. The reverse is Lungs.
Miscasts
Permanent deep one mutation (nictitating eyelids, webbed fingers, etc.)
Spell is permanent.
Greater mutation for duration of spell.
Gills are non-functional, and now you can't breathe.
The fish love you, maybe a little too much. Actions and visibility underwater are hindered by schools of fish, if any are nearby.
You have been chosen for a quest from Dagon (or other suitable entity). Details will come to you in your dreams.
Raft
Cleric 1
Providence sends a raft of sufficient buoyancy and size to support 1d4 person-days/level. It appears on the horizon drifting towards you, such that it can be reached by an unencumbered swimmer without issue (barring other circumstances). The form will vary but it will have no inherent means of propulsion. Some forms may include:
volcanic raft
iceberg
dense seaweed mat
carcass of a great beast
empty barrels & crates lashed together
low-lying fossil cloud
strange metal disc
empty shell of a dragon turtle
ants
Read Wakes
Magic User 1
Duration: 1 Round/level
Range: Self
In a perfect Newtonian world, information is never lost, it merely gets quieter and quieter. This spell lets you read the history of the ocean before you. Once each round, you may learn one of the following things:
What was the bearing of the most recent ship to pass here, and when was that?
What direction is the nearest stationary object?
Where and when did anything most recently break the surface of the water intermittently (like a whale surfacing or a stone skipping)?
etc.
This spell does not work in the rain or when the water is otherwise busy. If a question is asked again, you can read further back in history (e.g. the second most recent ship to pass).
Miscasts
Visions of the rain—severe headache incapacitates caster for 1d6 rounds/level. No information gained.
Echoes of creation—permanent deafness (this does not hinder the spell).
Ghosts of the flood—each day save or be possessed by an antediluvian ghost (with their own, worse CHA, WIS, & INT). They lose interest after a week of saves.
Harmony of nature—save or be compelled to join your ghostly whale friends swimming through the sea.
Bad point of reference—information given is actually about the future. This could raise issues about free will, but don’t let it bother you. At least it’s good information.
Transmission from the stars—1d4 permanent damage to a random ability score, and you learn a weird new spell.
Transmute
Magic User 1
Duration: Permanent
Range: Touch
When you learn this spell, roll for two materials, then roll for 1 more material/level. When you gain a level, roll again for an additional material. You can transmute the volume of 1 person/level from any one material you know to any other material you know. Allow saves as appropriate. Some materials include others, and this is not a mistake. For example, “stone” includes “marble”. You cannot choose to transmute to the more specific material if you do not know how.
Miscasts
Transmutation fails, and target is immutable to any future magic.
Transmutation fails, and you forget the target material.
Transmutation is successful, but only for 3d6 (1d4: 1-seconds, 2-minutes, 3-hours, 4-days).
Target goes to a random target material.
Target goes to a random target material, and you learn to transmute that material!
Transmutation is successful, but grafts itself to your body.
Materials (4d20)
If you re-roll a material, move up or down the list until you find a new one.
The table above is vaguely weighted with more common materials in the middle, so that hopefully you aren't stuck with "Transmute lava/ectoplasm/jade" as your only options. But I've been wanting to try out Spwack's thing, so you can also use this to roll flat across the whole table if you feel chaotic.