Osiris, the first mummy.
Long ago, in the land we call Egypt, there lived a sorcerer by the name of Osiris. Though mighty for his time, suxh that he managed to become king, he was not mighty enough, for in life his power would be equivalent to a modern day grade one sorcerer, this is in part attributed to his completely non-combat applicable cursed technique. Yet it is said cursed technique that allowed him to reach such a mighty status, and that will allow him to reach greater heights still. With the aid of his servants and countless binding vows, he underwent a process that would eventually develop into the process we call "mummification". And so as his corpse dreamt, he developed, changed, evolved, until he woke up. And lets just say, upon awakening his status as a deity became a lot less questionable.
Cursed technique: cultivation
Osiris could enter a deep sleep, during said sleep his cursed energy control, cursed energy reserves and cursed energy efficiency would increase. The longer the sleep, the greater the effect.
Journey to the Du'at:
Osiris' maximum output of his technique. Using countless binding vows and with the aid of his servant he entered a deep sleep while his servants mummified him alive. This allowed him to sleep for thousands upon thousands of years. Upon awakening he had the following abilities:
Gigantic ce reserves: comparable to the ce reserves of jjk and modulo... combined.
High ce efficiency: surpassing even that of Gojo
Cursed technique mimicry/creation: his control over cursed energy became so great that he could now mimic and create entire cursed techniques seemingly at will. Though for mimicry required some analysis of the technique first. If standard usage of a cursed technique is akin to letting electrcity go through an electronic device, then what Osiris does is by hand forcing the electricity to move through the empty air as if it is going through an electric device.
Weakness: as part of Journey to Du'at, most of his orgnas were put inside urns. Destroying these urns is akin to destroying his organs to the point rct would not be able to bring them back.