There are initially four different ways to use the Bestow Curse spell in D&D 5e. Those are as follows:
Disadvantage on ability checks and saves for one ability score
Disadvantage on attacks against you
WIS save or do nothing during a given round
+1d8 necrotic damage when you damage them
The spell normally lasts for a minute, but if cast with a 9th level slot, it lasts until dispelled, which is worth noting because the best curses last until dispelled. if cast with a 4th level slot, it lasts for 10 minutes. A 5th level slot is 8 hours. A 7th level slot is 24 hours. These all have their uses for creative players, but the best part of the spell by far is the encouragement to invent your own curses, which many players and DMs have taken as a challenge for their own creativity. So while it is certainly not new, it’s my turn to take a crack at it!
* - A curse marked with an asterisk is a 9th-level only curse due to its powerful detriment or long-lasting nature. But who is to stop you from enchanting an innocuous item with such a curse?
Hair Growth/Loss: You are cursed to grow hair at a rapid rate for the duration of the curse or else lose all of your hair (it grows back after the curse ends).
Mute/Deaf/Blind: You are rendered either mute, deaf, or blind for the duration of the curse.
Forbidden Speech: You are cursed to never speak about a certain subject, topic, or word for the duration of the curse.
*Rapid Aging/Deaging: You are cursed to either age by one year each day, or to grow one year younger each day. After you reach your final day, you die.
*Phylactery: Your fate becomes tied to a creature or object. If the creature or object is slain/destroyed, you die as well.
Ugliness: You are cursed with horrible deformity for the duration of the curse. You have -5 on Persuasion checks and Deception checks for the duration and are easily noticed and shunned by most humanoids of any race.
image source: Evil Dead 2: Dead by Dawn
Possessed Limb: One of your limbs (usually an arm) acts on its own for the duration of the curse, usually attempting to harm its host, harm others, or sow chaos.
Petrified Limb: One of your limbs becomes petrified and is unable to be used for the duration of the curse. It could turn into any solid mineral like stone, iron, glass, salt, or gold. Any damage it takes is retained once the curse is lifted.
Funny Looking: For the duration of the curse, anyone who you attempt to communicate with bursts into uncontrollable laughter. This does not prevent hostile creatures from attacking you, but prevents them from speaking.
Lichsight: For the duration of the curse, you can see the spirits of the dead. Whether real or illusory, you cannot communicate with them and you must make a WIS saving throw each round or become frightened and run in a random direction or cower in place (50%/50%).
Butterfingers: Each round while the curse is active, you must make a DEX saving throw. On a failed save, you drop whatever you are holding and cannot pick up or hold anything for the rest of the round.
Forgetful: You have a tendency to forget things. During the curse, whenever new information is revealed to your character, you have a 50% chance to not be able to remember it, even after the curse has ended.
*Lady of Shalott: You are doomed to die if you ever lay eyes directly upon another being, and must therefore look at the world through a mirror and avoid direct sight of others. The difficulty of maneuvering a hand mirror or the necessity to close your eyes effectively makes you blinded while in combat, imposing disadvantage on attack rolls.
Stingy: During the curse, you must make a WIS saving throw whenever you intend to part with money. On a failed save, you opt not to spend your money on it. You cannot make another such save for the same purchase, even from a different seller.
Empty Coinpurse: You are compelled to buy things until all of your wealth has disappeared. You will even go so far as to barter your own goods once out of money. Whenever you find something for sale, you must make a WIS saving throw. On a failed save, you will do anything you can to attempt to purchase it or trade for it. Only if the seller refuses three times will you give up.
*Baleful Polymorph: You are transformed into a small creature or tiny animated object for the duration of the curse. You retain the ability to speak using a disembodied voice emanating from the creature or object, usually paired with animation like a moving mouth (if a creature) or a mouth-shaped part (if an object; like a book opening and closing its covers and such). You can move with a move speed of 10 ft. per round if an object.
image source: Star vs. the Forces of Evil
Talking Tumor: You grow a tumor-like second head that can speak that embarrasses, berates, or otherwise annoys and inconveniences you. It has +6 for Persuasion, Deception, and Intimidation checks, helping it be a complete jerk.
Evil Aura: Plants within 15 ft. of you wilt and turn brown or gray and animals within 60 ft. feel afraid or threatened by you for the duration of the curse.
Bad Taste: Eating food or drinking water causes you to become poisoned for 1d6 hours, or for the duration of the curse.
Bad Luck: Whenever you have advantage for the duration of the curse, you instead have disadvantage.
*Prophecy: You become destined to die under certain circumstances. Whenever it is possible for those circumstances to be met, you must make a relevant saving throw (falling boulder? DEX save. Poisoned apple? CON save. etc.) or begin dying. The victim cannot be threatened by the curse more than once every 2d4 hours. The curse will take increasingly convoluted measures to try and make the prophecy come true the longer the curse lasts.
*Guardian: The victim is polymorphed into a hostile creature of CR 6 or less. The victim is given some sort of command like guarding a location or spreading suffering, and will continue to do so until the curse is lifted or they are slain. They revert to their regular form if they are slain. The victim cannot communicate and is hostile to all creatures. The creature becomes immune to the charmed condition.
image source: Sleeping Beauty by Henry Meynell Rheam
Slumber: You fall into a deep slumber and cannot be awoken until the curse is lifted.
Eternal Rest: If slain while under the curse, you cannot be resurrected by any means even after the curse fades.
Phantasm: You believe that you have been polymorphed into a small creature (like a toad or chicken) and act as such for the duration of the curse.
Unquenchable Thirst/Hunger: You feel eternally hungry and thirsty. You must make a WIS saving throw whenever you encounter food or drink, no matter how dangerous or questionable it might be (swamp water, obviously poisoned food, moldy bread, etc.). On a failed save, you consume it.
*Obedience: Whenever someone you can understand issues a verbal command to you while you are cursed, you are compelled to obey. You may attempt a WIS saving throw to resist a given command for one minute.
Hold your tongue! (Ella Enchanted)
Magical Immunity: You become immune to nonharmful spells for the duration of the curse. Spells cast by enemies or damaging spells still affect you, but healing spells and buffs do not.
Unhealing Wound: A wound you have will never heal. Your maximum hit points are reduced by 2d4+the caster’s spellcasting modifier. This curse cannot reduce a creature’s health to 0 in this way.
*Wandering: While under the effects of the curse, you are compelled to wander. Each day at dawn, you must leave and never return to the same city/town or 2.5 mile radius (if in the wilderness).
*Deadly Descendants: All of your descendants are cursed to kill their birth parents, whether intentionally or not.
*Lonliness: You are cursed to die alone. Anyone you become romantically close to or close friends eventually leaves or dies or meets a horrible fate.
*Gargoyle: You are petrified during the daytime and return to normal at night for the duration of the curse.
Voyager: You cannot set foot on dry land for the duration of the curse, taking 1d6 psychic damage each round that you do.
Yes, there’s always a Wish spell or a Remove Curse spell, but I often believe that if any cleric can remove a curse it undercuts the drama of the punishing spell. Instead, use an alternative way to remove the curse. Most of it depends on how the curse was placed and the reasoning behind it. For instance, if you refuse to give a gypsy shelter from the cold in your luxurious castle, you might get transformed into a beast until someone falls in love with you. Here are some ways that one could feasibly break a curse (if the situation allows).
Give back an item that was stolen from the caster
Complete a quest or mission for the caster
Kill the caster
Pass the curse onto someone else (through some deliberate means like a handshake or kiss or losing a wager)
Seek out a powerful extraplanar being
Seek out special magical ingredients for a cure
Find a loophole in the wording of the curse (either through tricky wording or by finding a liminal loophole. “No man of woman born” could exclude a man born by C-section. “Neither day nor night” could exclude twilight)
Change your alignment (an evil or chaotic character learns to be good or lawful.)
Change your ideal or traits after learning some sort of lesson
Overcome one of your flaws.
Let the curse run its course instead of fighting it.
Find true love/True love’s kiss etc.
Prove your worth to the caster
Atone for past sins
Selflessly risk your life for someone else
Convert a creature to worshiping the caster’s deity
Avenge the caster
image source: Disney’s Beauty and the Beast (1991)
Feel free to use this list and add to it your own ideas for curses! There are so many possibilities that it’s never out of the question to find a new curse that uses arbitrary magical rules to drive the plot of a story. I guess that makes curses the sitcoms of the fantasy world.