Because You Saw a Ghost

 1. All you can smell is burning.

2. The DM rolls twice as many encounters but half of them aren't real; only you thought something was approaching.

3. Every person has white hair and black eyes for you now.

4. Each creature you kill becomes a voice in chorus that questions your actions.

5. Perhaps they died bound or hung, but you no longer see rope.

6. You only heal if you carry something dead with you.

7. You can see lies.

8. You faint if left alone.

9. Gold smells like rotting flesh.

10. Everything is offkilter; only odd numbers work for you (to hit, it must be an odd number, to do damage it must be an odd number, to win initiative it must be an odd number, etc.).

11. Metal passes through you.

12. Animals are terrified of you.

13. Your clothes and gear seep blood constantly.

14. Every person that looks at you mistakes you for their most recently dead relative.

15. Food is as heavy as lead for you.

16. You can no longer see creatures that have drawn your blood.

17. When you speak, it comes out in an ancient, dead language.

18. No fire you make stays lit.

19. You no longer remember names.

20. Dead things regain life for as long as you touch them.

Curses for Mages

1. Each syllable the scholar utters causes a hands-width of dark water to rise from under their feet.  This water fills an area as far as they can see and will only recede a turn after the last syllable spoken.
2. Each new creature the scholar encounters must be documented in writing and they feel compelled to tell each new acquaintance about every creature on that list.
3. The scholar feels compelled to make a list of actions to take in the next dangerous encounter and will abide by them when the time comes.
4. If the scholar stops moving, anything they are touching, clothes, chairs, food, begin to get hotter and hotter until those things catch fire and burn.
5. The scholar has acquired a great fear that they will read a forbidden book and, so, they read no books.
6. The scholar will feel compelled to gather herbs for study and fill their pack full to overflowing, and be reluctant to discard a single herb, even to make room for food or gold.

Numberless Curses

 These are curses on weapons that are not about -2 to hit or damage, but more about limiting the fighter tactically.  It may even be interesting to have weapons that have a bonus to hit and one of these curses and then let the player decide whether using the weapon is worth the trouble.  This weapon is cursed so that you must always: 

1.     attack last, after all allies and foes. [Sloth]

2.     attack only once per battle. [Sloth]

3.     attack only until you wound a foe, then stop. [Sloth]

4.     attack a foe only after it has been wounded by an ally. [Sloth][Envy]

5.     attack only one foe until it is dead and keep beating the corpse until the battle has ended. [Wrath]

6.     attack a foe, switch targets and attack that foe, switch targets etc, until the battle has ended. [Wrath]

7.     attack only foes that are also being attacked by an ally. [Envy]

8.     attack only foes that have attacked you. [Vainglory]

9.     attack only foes that have attacked an ally. [Sloth]

10.  attack only foes that have wounded you. [Vainglory]

11.  attack only the last foe to have wounded you. [Vainglory][Wrath]

12.  attack only foes that have wounded an ally. [Sloth][Wrath]

13.  attack only when unarmored and shieldless. [Vainglory]

14.  attack only while allies fight alongside, otherwise you surrender. [Sloth]

15.  attack only alone, never with others. [Vainglory]

16.  attack only unaware targets. [Sloth][Cowardice]

17.  attack only after shouting your intended target. [Vainglory]

18.  attack only the most threatening foe—the largest, most experienced—then stop when they are dealt with. [Vainglory]

19.  attack only the weakest foe—the smallest, most frightened—then stop when they are dealt with. [Sloth][Cowardice]

20.  attack only when begged by an ally. [Vainglory]

 

For some reason I started thinking of these curses in a framework of traditional Christian sins, like the knight that wielded the magic sword last was an anti-saint that was reeking of pride.  Sorry if that's a distraction, there are other ways to frame curses as “bad” as I realized when I noticed that cowardice, which is often reviled, is not one of the seven deadly sins, nor selfishness.  Also, I like the term vainglory here better than pride for boastful, showy fighting.