"Origin: Japan. A mountain-sized serpent with 8 heads. It's said that trees and moss grow on its body, red eyes, and festering belly. It was defeated by Susano-o when Kushinadahime was about to be sacrificed to it. The sword that emerged from tis belly was called Ameno Murakumo."
—Shin Megami Tensei A-Mode DDS Dictionary
Shin Megami Tensei IMAGINE
Yamata no Orochi appears as a special boss in Ueno's Kuchinawa Cave, summoned by connecting with all the plasma on the field and then killing the Onamuchi field boss. He also acts as the final boss of the Virtual Beach's Izumo island, as well as a regular Daily Mission boss for players over level 95. By offering golden sake, players are able to summon a stronger variation for a chance to obtain the ability to fuse him. He is a special triple fusion of Quetzalcoatl, Nidhoggr and Raja Naga and learns a special fire affinity spin skill at level 98.
As a playable demon, Orochi can be found in the wild at InfernalCamp Ichigaya or created through fusion. There are no special requirements to summon him, apart from Flynn being at least level 60.
Apparently as an error in one of the game's foreign localizations, his Compendium entry is actually that of Hoyau Kamui, who does not even appear in this game.
Shin Megami Tensei IV Apocalypse
Orochi is needed for the challenge quest "u have a guest!!!," in which Nanashi must fuse Yamata-no-Orochi and present him to Take-Mikazuchi in the Fairy Forest near the base of the great tree. Take-Mikazuchi will then use the Ame-no-habakiri to kill Orochi, with the blade transforming into the upgraded Ame-no-murakumo.
Orochi can teach Nanashi the Bufudyne, Agidyne, and Megaton Press skills through its Demon Whisper. It benefits from learning Physical, Fire, Ice and healing skills. Unlike most demons, its attack also strikes all enemies present.
Like in Shin Megami Tensei IV, Yamata-no-Orochi's compendium entry describes a different demon entirely.
Devil Summoner: Raidou Kuzunoha vs. The Soulless Army
In Persona 4 The Animation, Yamata-no-Orochi represents the bond between Yu and his classmate Ai Ebihara. After completing his Social Link with Ai, Yu fused the necessary Personas to summon Orochi, using its power in the battles against Shadow Kanji and Shadow Mitsuo.
In the True Ending special, Yamata-no-Orochi was summoned to defend Yu against Yoshitune's attack, as well as bring a message of support for Yu from Ai.
Orochi is two separate demons as Orochi and Yamata no Orochi in the series. In the English versions of Dark & Light they are known as Orochi and Octorex.
Devil Children Black/Red Book
Rank fusing Orochi seven times can have him rank up to Yamata no Orochi.
"Huge snake-like demon that can generate large earthquakes simply by moving."
Octorex can perform the combo Wyrm Breath with Lindwurm or Wing Rox.
Digital Devil Saga: Avatar Tuner
Orochi is found in the Samsara Tunnels underneath Anahata. One of the doors to his chamber has been severely dented beyond operability and he remarks that his prey recently escaped before he could devour them. Not wanting to lose another meal, he immediately sets upon the party as they try reach the middle of the bridge in front of him.
Orochi is set apart from other bosses in that he gets 8 press turns per round and has a noticeable limit on his MP pool. He will respond immediately to -kaja and -nda spells with Dekaja and Dekunda, which will seriously cut into his MP. Once he runs out, he will stick to using Mad Rush every press turn unless he has enough MP to use MP Thief, which he will use to start another magic skill barrage if allowed. The Null Poison auto skill will protect the party from his Foul Breath attacks and Null Mute skill will prevent him from starting up another magic barrage.
After Orochi is defeated, the party can continue deeper into the tunnels and reach a seperate area of Ajna. In the upper floor hallway, a woman who was presumably the victim Orochi mentioned can be found but sadly she has passed away. The party will obtain the Red Ring key item upon examining her.
Devil Survivor 2
"A giant snake with eight heads and eight tails that appears in the Kojiki. It demanded a sacrificial maiden each year, but Susano-o got it drunk and killed it with his sword."