ok the dark prison is a un-escapable prison in the netherealm.where all the bad people that die go when they compete in mortalkombat or if ur a fugitive in the netherealm.( example kano, jerek, tayna) ok so the dragon king arrises. and takes over the dark prison. he tries to eliminates anything/anyone that could be a threat to him or his plans. so he throws some of the mk warriors in the jail so they dont posse as a threat to him. so he throws kitana and the elder god fujin in the prision along with stryker.dragon king does not car about jerek because he was a good guy in mk4 and hsu hao was a traitor drahmin was also a traitor to shang tsung .so the dragon king doesnt want those type of peepz helpin him. he fears that they can easily turn on him also. so he keeps em in the prison. he also uses the prisoners as bait. to lure the rest of the mk warriors to the netherealm.