Shinnok: Getting Better Treatment Than MK4/Gold For A Villain!
Shinnok was first introduced in the lame MK Adventure game MK Mythologies: Sub-Zero and he became the final boss in Mortal Kombat 4 and in its Dreamcast only upgrade, Mortal Kombat Gold as a playable character who was also the final boss. He was introduced as a fallen Elder God who is now the ruler of the Netherrealm and Raiden's sworn rival. He would be the Loki of the Mortal Kombat universe. In Chinese mythology, Shinnok would be the King of Hell, in the Buddhist pantheon, he would be equivalent to Mara, the ruler of the Buddhist Hell.
In the Mortal Kombat 4 arcade, Shinnok was the final boss and Quan Chi was the sub-boss. Shinnok had no moveset of his own and he only imitated other characters' moves. However the CPU Shinnok only used default punches and kicks, making him too easy a final boss. I felt it was stupid to let the god of Hell be treated in such a way.
Mortal Kombat Armageddon did another disservice to the god of Hell. Well it was later revealed that the "Shinnok" you are using is just a clone. However, it was no excuse not to make him a sub-boss character before the battle with Blaze. I mean, he freaking masterminded a lot of events in Armageddon like reviving Onaga and the events behind Daegon's corruption. He had his own moves in Mortal Kombat Armageddon as well like a giant fist projectile, teleport and dash.
However it seemed hew as actually responsible for one event... everyone's reincarnation after Armageddon. As you see, everyone was killed off during Armageddon but before they were reincarnated, Raiden shouted, "He must win." to which Mortal Kombat was rewritten differently in their next lives. Shinnok may have masterminded those events considering that Quan Chi said, "Your plan worked into perfection, Lord Shinnok." in the ending of Mortal Kombat 2011's story mode. Later, it's discovered that he masterminded the events that would have the Earth's defenders (minus Johnny Cage and Sonya Blade) to become part of his army as revealed in Mortal Kombat 2011.
Mortal Kombat X would feature Shinnok with a demon form he deserved to have in the fighting games... he had that in Mortal Kombat Mythologies which sucked, so why not in a game that rocks? While MK4/Gold did no justice to him, this time he's up to something. He's up to using the Jinsei energy (or life energy in Taoism) in order to further his own agendas. Shinnok has his own moves while he and Goro will be playable, he reveals an Inferno-like form for his final form. He absorbs the Chi involved in Earthrealm, which disturbs the Tao, creating him into this evil form that would prove to be a challenge to players in a one round only to beat guy.