The first long-range Stand revealed in the series, Hierophant Green fights at a distance and is capable of unraveling into tentacles and unleashing a brilliant blast of emeralds known as the Emerald Splash.
Hierophant Green is a humanoid Stand of average build clad in several light-colored pieces of armor all over its body with much of its body still exposed. Its armor includes a mask that can be broken to reveal a mouth. Several of Hierophant Green's joints are mechanical, and its eyes are as well. The body is green and covered in a web-like pattern that Jotaro Kujo describes as reminiscent of a shiny melon.
All of its body is capable of unraveling into tentacles covered in complex patterns. The tentacles can vary in size and even be connected to each other.
Hierophant Green has consistently been portrayed as various hues of green while its armor and eyes vary throughout media.
The series is known for alternating colors between media, the information presented below may or may not be canon.
Armor(Light mint green)
Body(Light green and black)
Although Hierophant Green typically does not emote and only speaks when Kakyoin uses it to, he states that it hates open spaces and loves to rip things apart.
Hierophant Green is the very first Long-Distance Stand shown in the series, and it has a large number of abilities to assist it in combat and scouting. However, the Stand is relatively weak in direct hand-to-hand combat, as a trade-off for its great distance-based abilities.
Hierophant's coiled body is often underestimated
As Hierophant Green's original appearance is not humanoid, but instead just a group of connected membranes, it is able to unravel itself into multiple long strings for multiple purposes such as acting like ropes, avoid damage without hurting Kakyoin himself (as shown in the battle against Death Thirteen) or weave out a network of sensitive strings that detects the enemy's movements, as during the battle with DIO.
As such, Kakyoin can control how Hierophant Green unravels, creating strong ropes or unraveling them into invisible strings. A single string has the ability to sense when someone is touching it and can attack either automatically or at Kakyoin's command. When a string is broken, Kakyoin is unharmed, but attacking a sufficient number of them or Hierophant Green's main body will harm him.
Hierophant Green invading Death Thirteen
Hierophant Green is capable of sliding its coils into a person's body, allowing Kakyoin complete control of that person. This serves to protect Hierophant Green and Kakyoin from attacks if his opponent is someone unwilling to harm the innocent. Additionally, he can completely destroy the controlled being's air passage as he emerges, as well as the host's internal organs. When this ability is first used, Kakyoin is shown holding a marionette by the strings, but it is likely just for dramatic effect.
The Emerald Splash is Hierophant Green's most powerful ability. It gathers energy into its body, causing it to glow bright green, before firing off a large amount of energy which takes the form of emeralds. Before the blast is fired, a green slime-like material (water-like in the anime) is produced by Hierophant Green's hands, a byproduct of the large amount of energy the attack is giving off.
The blast's range and shotgun-like dispersion, along with its incredible destructive power and high speed, make Hierophant Green an extremely capable combatant. Interestingly, it seems that though this blast is quite powerful, it doesn't seem taxing on either Kakyoin or Hierophant Green. However, the likes of Star Platinum or even a Vampire can easily block or deviate the attack.
During the Weekly Shonen Jump serialization of Kakyoin's introductory arc, his Stand was originally named "Hierophant Emerald" (法皇の緑,Haierofanto Emerarudo). The name was changed to Hierophant Green after Kakyoin joined the Joestar Group, and was later corrected entirely in the tankobon release of the aforementioned arc.
Hierophant Green ended up green because Araki wanted some color balance between the allies and enemies. Green reminded him of melons, and he was really into green at the time as he used the color in several illustrations.