Physically Altering Curses

Question

In a custom campaign, I placed the characters in "The legendary library of Oghma" where all the books were history, not the writing about things that happened, but the things themselves. Basically it was a library of the world's events. There were some notes scattered through the library to explain what the books were, how to leave the library, and consequences for harming the library.

In the notes, an NPC who burned a book was cursed and eventually became the voice of Oghma, a dragon that watched over the library. There was a split in attendance, and some people who were coming regularly stopped coming for a while.

THE SITUATION
So the core group made it out unscathed, then two people who had started in the library came back and burned several books and a painting. I don't really want to turn them into dragons, but I was wondering what rule sets there were to help handle this situation.

Are there any curses for players that change them in interesting, but still playable, ways?

Answer 1

You don't actually have to change anything.

The reason I say this is actually right here (emphasis mine):

"...was cursed and eventually became..."

My recommendation is to leave the curse as is, and start very slowly (over years) changing them into dragons.

This leaves them playable, and also doesn't modify the curse. Just have them start developing scaly skin. Over time, actually have them grow some scales. You can also give them other nifty little effects over time like:

1. Craving raw meat instead of cooked meat.
2. Developing bony ridges on their shoulders (wings eventually)
3. Nails that are hard and sharp, and teeth becoming pointy
4. .... and just more and more dragon attributes.

Basically, make the curse last a really LONG time. Interesting changes I would use this curse to make:

1. The scales would eventually develop to make the player a half-dragon (while they were still playable) and grant them resistance to whatever colour dragon they are becoming.
2. The talons and teeth would count as 1d4 unarmed weapons.
3. The wings would eventually be usable (around level 9).

And that's just for starters. As for breaking the curse: Wish spell, remove curse (or if you want it to be a lot harder than that), restoring the destroyed works.