Orochimaru's Juinjutsu

Orochimaru commonly uses cursed seals on his most powerful followers. To apply a cursed seal, Orochimaru needs to actually bite his intended target. Because he has sharp fangs and an extendable neck, this is a relatively simple task. The seal then appears somewhere on the target's body, and they subsequently lose consciousness. Sometime later, should they survive, they will awaken with the first level of the seal active and be enraged due to the seal's influence. The seals work by forcibly drawing chakra from the user's body, giving the user a chakra capacity beyond what they would normally be capable of, as well as increased physical performance as a result of the increased chakra capacity.

Overview
The seal has two different levels, and the types of transformations differ from seal to seal. When inactive, the seal is simply a black tattoo on the user's body. Orochimaru has a wide array of cursed seals, so the appearance of the seal will usually vary from user to user. Each seal always has three identical marks arranged in a circular pattern. When first activated, the marks on the seal glow and replicate, spreading over the user's body. This is known as the first level of the seal. The degree to which this occurs is dependent on the user, and the degree to which it spreads is proportionate to the overall effect it has. Normally, the wearer of the seal will also experience slight pains during the activation of this level. The second and final level of the seal causes the black marks to completely envelop the user. This is followed by an unnatural alteration of the user's body, with the only common features being yellow eyes with a black sclera. When in this level, the seal eats away at the user's personality, driving them to madness if used too long. It also takes quite a toll on their body, since they are being mutated by the seal. Aside from the first and second levels of the seal, skilled users of the seal are able to perform partial transformations in which the aforementioned mutation caused to the users body in the level two state can be used without completely altering the entire body. The power of the cursed seal can even synchronize with the user's regular body with extended use (as stated by Sasuke during his second fight with Naruto), increasing the power of his/her natural state.

Because the seals forcibly draw chakra from the user, they will often kill the user when first applied. Orochimaru has averaged a ten-percent success rate when applying these seals. Additionally, even if the user survives, their body will not be able to easily control the power of the seals given to them. To compensate for this, Orochimaru developed the Seishingan drug. The drug forces the user's body to become accustomed to the unnatural increase in power, but also kills the one who takes it. The sealing jutsu and  are used to keep the drug from killing the user by placing them in a temporary death state. Though the Sound Four were the ones to perform the technique, it stands to reason that they weren't the ones that created it.

Orochimaru developed the cursed seals through experimentation on a prisoner named Jugo, whose body naturally produces an enzyme that triggers a state on which the cursed seal is based. The difference between Orochimaru's seals and the unrefined enzyme are the effect they have: while the cursed seal is controllable, the unrefined enzyme produces uncontrollable rage in those exposed to it, including Jugo himself, and the effects cannot be controlled.

Cursed Seal of Heaven

 * Wearers: Sasuke Uchiha, Anko Mitarashi

Cursed Seal of Earth

 * Wearers: Kimimaro Kaguya

Sound Four's Cursed Seals

 * "Wearers:' The Sound Four