i think that in arcade mode after you defeat all the normal fighters you should get 2 fight against 3 sub bosses and then the sub boss

kintaro- came back 2 avenge goros death but was enslaved by the dk

moloch- after quan chi's death shang tsung granted him supreme power and gave him several souls and now moloch is far stronger and has new powers and betrayed shang and is now serving the dk

chimera- the 3 headed beast that serves the dk.

the dragon king- a great dragon that was reborn upon the hatching of the dragon egg he is now the ruler of the netherealm after quan chi and shang tsung's deaths.

Boon if you're reading this then add this and it would make deception the greatest mk game ever!!!