Users can increase their own physical and spiritual prowess via a negative supernatural affliction they have, this power usually activates when the user exhibits strong negative emotion or distress. As the user masters the power, the negative effects of the mystical affliction become less apparent as the victim's body becomes more assimilative to the curse. When the curse or affliction is removed from the user their powers will disappear until the curse is re-initiated.
Legendary Hero Curses Series (Rising of the Shield Hero)
Mark of Cain (Supernatural)
Akame (Akame ga Kill) activates Murasame's trump card which imbues her body with a curse that increases her strength and speed tremendously.
For all of its downsides, the Sohma family curse (Fruits Basket) does grant some benefits beyond normal humans to the Zodiac members, such as enabling them to commune with and control animals of their Zodiac sign...
...giving Kyo the agility of a cat...
...and Kagura the strength of a boar.
Every Demon in Tartarus (Fairy Tail) can use Curses instead of Magic.
Canis Lykaon's (Highschool DxD) darkness based powers originates from the soul of Lycaon King of Arcadia who was cursed by Zeus into a werewolf.
Yuji Itadori (Jujutsu Kaisen)
Miroku (InuYasha) has been able to harness his Wind Tunnel curse as a potent weapon.
The increased speed of growth of the Zombie Tattoo put Alviss (Marchen Awakens Romance) in a brainwashed state where his magical power and physical strength greatly increase.
The forbidden power of Ghost ÄRMs (Marchen Awakens Romance) curse the user's body, allowing them to change their appearance at will.
Jūgo (Naruto) is the source of the cursed seals.
Sasuke Uchiha (Naruto) empowered by the Cursed Seal of Heaven.
The demonic curse on Ashitaka's (Princess Mononoke) right arm also bestows him with superhuman strength.
The Shield of Wrath (Rising of the Shield Hero) is one of the Curse Series weapons of the Four Holy Hero.
After being trapped in the Earth by Aku, the "Lava Monster" (Samurai Jack) developed the power to manipulate the earth around him to his liking.
After Ash Williams spoke the wrong incantation, Vampirella (Vampirella/Army of Darkness) was sent back to the Middle Ages and transformed into a powerful demonic, bat-like monster by the Necronomicon Ex-Mortis...
...a form she could later switch between on command after eating the page the curse was written on.
Michael Myers (Halloween) is the bearer of the Curse of Thorn, granting him superhuman strength and immortality, but also filling him with an uncontrollable rage that drives him to kill his family members in the hopes that the rage will abate.
Cursed by the Sisters, Hanzo (Kubo and the Two Strings) was transformed into...
...an anthropomorphic beetle, granting him the power of flight, six limbs and the ability to hold his breath for extended periods of time.
After being executed via the curse of Hom Dai, Imhotep (The Mummy) was granted numerous supernatural powers, most notably his immortality and power over the Plagues of Egypt.
Hector Barbossa (Pirates of the Caribbean) was cursed by The Cursed Aztec Gold, which transformed him and his entire crew into undead immortals,...
...preventing all of them from dying and making them virtually indestructible, while also causing physical limitations to their lives.
Jack Sparrow (Pirates of the Caribbean) gained the same curse from The Cursed Aztec Gold as Barbossa and his crew by secretly stealing one of the cursed coins.
Barbossa's pet monkey Jack (Pirates of the Carribbean) was also affected by the Cursed Gold.
Delphine LaLaurie (American Horror Story: Coven) was cursed with immortality by Marie Laveau
Rumpelstiltskin (Once Upon a Time), empowered by the curse of the Dark One, gives him magic and immortality.
When Ryu Hayabusa (Ninja Gaiden) was infested with the deadly Grip of Murder Curse in his right arm, the curse empowered him with an incredible increase in strength at the price of immense pain.