User can place a curse on whatever they wish (people, places, objects, etc.). The exact effects can be nearly anything the user desires, ranging from minor annoyances to tortuously extended death.
Among the most common effects are misfortune/bad luck, various sicknesses, infertility, physical defects/ugliness, etc. when affecting people, breaking or working wrong or causing problems when used on objects and tendency to draw various disasters for places. Traditional magical curses include transforming the victim fully or partially into an animal/monster that fits the offense, blood-lust, insanity, unstoppable rages, unhealing wounds, misshapen/inhuman offspring, and a whole host of other effects.
Genshirou Saji (Highschool DxD); via Balance Breaker
Lee (Your Pretty Face Is Going To Hell)
Cursing Camera (Doraemon)
Hex Bag (Supernatural)
Darkness ÄRMs (Marchen Awakens Romance)
Amulet of Avalor (Sofia the First)
Jusenkyo (Ranma 1/2)
The Eggplant Wizard (Kid Icarus) curses people by turning them into eggplants.
The Cursing Camera (Doraemon) creates a voodoo doll of the person in the snapshot, basically cursing the victim to be at the complete mercy of the doll's holder.
Orochimaru (Naruto) can force his subordinates and subjects into mutation via a Cursed Seal.
Hidan's (Naruto) Jashin ritual will put anyone under his curse.
The Regent of the Mask (Ninja Gaiden 3)
Ryu Hayabusa has been afflicted with the Grip of Murder curse by the Regent of the Mask.
Every Demon in Tartarus (Fairy Tail) can use Curses instead of Magic.
Miku Hinasaki (Fatal Frame) has been afflicted by the lethal Rope Curse by the spirit of Kirie Himuro.
Naraku (InuYasha) is well-versed in various curses and black magic...
...the most notable of which being the Wind Tunnel curse he placed on Miroku's family.
The house of where the Saeki family lives, Kayako (The Grudge) will curse them when the house is entered and will kill them, along with spreading the curse to anyone who comes into contact with the cursed ones.
Est (Spirit Elementalist's Blade Dance) has her nickname "Demon Slayer" but is actually cursed demon sword that had absorbed those various curses and pass them onto its master, result in taking user's life.
Storyteller (Valkyrie Crusade) uses all sorts of dummies to place curses and cast spells.
Talisman (Valkyrie Crusade) the goddess of curses.
Ingrid and Freya Beauchamp (Witches of East End) cursed to die young and be reborn to relive it again and again.
In his final moments, Demise (The Legend of Zelda) cursed the bloodlines of Link and Zelda, vowing that an incarnation of his hatred would forever hound their descendants.
As a mockery of Sariatu's love for him, the Sisters (Kubo an the Two Strings) cursed Sanzo, turning him into an anthropomorphic beetle.
Anyone who has sex with Lee (Your Pretty Face Is Going To Hell) is cursed with elephantiatis of the nuts.