Ryu Hayabusa

A character from Ninja Gaiden.

Season 5
A mysterious character that shows up in the Death Game when La Parka announces the existence of dolls, being possibly one.

Episode 8

Emerges from shadows in order to protect his master Tommy Wiseau, but ends up jobbing in under a minute.

When Mr. X attacks Wiseau again and Miles Edgeworth question hims, it is actually revealed that Wiseau is in reality Edward Richtofen under the effect of The Parasite, and this is not the real Ryu but is actually a being developed after the parasite's merged form like some sort of off-spring by SC.

Episode 10

When Richthofen, now freed from the transfiguring properties of the parasite, is put into a deathmatch against the very being modeled after him, and is executed.

Episode 12

Granted he was never a participant in the death game, and he was not destroyed along with the dolls, he's likely one of the few beings who survived it to the end.

Season 6
However, nothing is known about him or his plans after the collapse of Universe 2K20.

Episode 12

After the death game, likely with the help of BANS, he escaped the crumbling universe an was taken to a lab (possibly an SC one), either willingly or by force, and carrying together with him was Richtofen's body, along with the Summoning Key. Using it's power, all three were combined into a being now known as God-Emperor II. While training his newfound powers in there, Rumble-17 began and leveled the entire place, killing everyone inside but him, which would make him known as someone whose death escapes him.

He became known as the greatest assassin in all of BANS Army, rarely sighted but always ending his target with his power. He became contacted by The Circus to kill Suou Tatsuya for a very "personal reason", but BANS tried to discourage him from taking it due to carrying the very important Summoning Key within him, but he decides to anyway since it's impossible for him to die.

When he encounters Tatsuya, he is so vulnerable and none-the-wiser that he tells him exactly how much he will enjoy killing him, but before he can act, Power crashes Tatsuya's motorcycle on him, killing him instantly. She also eats his Summoning Key.