The Frenchman's Curse

A parasitic spell for LotFP or similar.

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.

References

Talking to your spells:

• Spell Consultation
• "It's still magic even if you know how it's done"

Parasites with intermediate hosts:

• Toxoplasmosis in Rodents

Memetic diseases:

• The Gardens of Ynn, probably