The Curse Seal was developed by one of the Legendary Sannin, Orochimaru. The seal is used as a form to control the person and a technique to literally kill the person through suffering. A person with the curse seal only has a 10% chance of surviving. If the evil curse seal has consume a person's body, that person will gain tremendous dark chakra and increase their strength and speed, giving them level 1 curse seal. The curse seal can active at anytime. A person's will is able to stop the curse seal from spreading or active it. To obtain level 2 curse seal, a person must lost his life, not actually died but fake death. The person will eat the Seishingan drug and is placed inside a container, sealed with seal symbol. The drug will make the person fall into a coma, much like near death. When the Seishingan drug have fully consume the person, that person has achieved level 2. Anyone that stay in level 2 form for a certain amount of time will lose themselves forever and become evil.

Sasuke Uchiha

Sasuke Cursed SealCurse Seal
Sasuke's curse seal is known as the Heaven Seal. It is the strongest and powerful of all the curse seal. He received the mark during the 2nd stage of the Chunin Exam. It was merely a test for Sasuke to see how strong an Uchiha bloodline is.
Sasuke Cursed LV 1Curse Seal Level 1
Sasuke achieved level 1 curse seal when the curse seal had consume his body. It took over his body during the fight against the 3 Sound Ninja, giving him big amount of chakra. The spreading of the curse seal will active the level 1 curse seal.
Sasuke Cursed LV 2Curse Seal Level 2
After taking the Seishingan drug and placed inside the container, the drug was able to fully consume Sasuke and somewhat killed him. He must died to obtain level 2 curse seal. In this level, Sasuke light brown and grew longer hair and has 2 wings. This form makes his Chidori (Lightning Edge) turn black instead of white. Sasuke doesn't stay in this form long because he doesn't want to lose himself forever.

Anko Mitarashi

Anko Cursed SealCurse Seal
Mitarashi Anko must of received the curse seal when she was young. Orochimaru used her to accomplish his own goal and never took care of her as his student. Anko survived after receiving the curse seal but we never saw her in at level 1 curse seal. She is able to control the curse.

Jiroubou

Jiroubou Cursed LV 1Curse Seal Level 1
Jiroubou probably received the curse seal when Orochimaru was scouting for an army. The curse seal spread in a triangle style. His strength increases.
Jiroubou Cursed LV 2Curse Seal Level 2
His level 2 curse seal grant him 10 times the normal strength. His skin turns reddish and his hair is extended longer.

Kidoumaru

Kidoumaru Cursed LV 1Curse Seal Level 1
Kidourmaru probably received the curse seal when Orochimaru was scouting for an army. The curse seal spread in a vine style. He is able to control and manipulate spiders and spider webs.
Kidoumaru Cursed LV 2Curse Seal Level 2
His level 2 curse seal turn him into a werewolf like. His skin turns red and has a fluffy hair and contain a third eye on his forehead. His body is protected and surround by spider web. His able to make bow and arrows with his mouth and shoot them.

Kimimaro Kaguya

Kimimaro Cursed SealCurse Seal
Kimimaro's seal is known as the Earth Seal. It is the 2nd strongest and powerful as the Heaven Seal. He probably received the curse seal when he was a wandering kid. He is able to manipulate his bone structures and use them as weapons.
Kimimaro Cursed LV 1Curse Seal Level 1
The curse seal spread like a maze. He possessed this level cursed seal when he was little.
Kimimaro Cursed LV 2Curse Seal Level 2
His level 2 curse seal turn him dinosaur like creature. He has a tail and has 3 large bones sticking from his spinal cord. In this form he able to use his spinal cord as a weapon and create a flowering spear.

Sakon - Ukon

Sakon Cursed LV 1Curse Seal Level 1
Sakon probably received the curse seal when Orochimaru was scouting for an army. Sakon has a twin brother name Ukon that lives inside him. He's able to enter a person's body and destroy the person's cell from the inside. Ukon surface when Sakon summon him or on his own will. The seal spreads like a bold line.
Sakon Cursed LV 2Curse Seal Level 2
His level 2 curse seal, Sakon and Ukon each grow a horn on opposite side and a metal armor on the opposite side of the horn. In this form he is able to summon Orochimaru's strongest defense, the seal gate Rashomon.

Tayuya

Tayuya Cursed SealCurse Seal
Tayuya probably received the curse seal when Orochimaru was scouting for an army.
Tayuya Cursed LV 1Curse Seal Level 1
The seal spreads in a zigzag line.
Tayuya Cursed LV 2Curse Seal Level 2
Her level 2 curse seal, Tayuya grow 5 horns and turn dark brown. In this form she is able to use her Genjutsu techniques, the Demonic Flute: Illusion Harmony.