Remeber The game eternal champions, Challenge from the dark side? Well in that game You could do a finisher where you summoned the final boss and he killed the character in a unique way. I think MKD could do something like that. Where a demon or something like that is summoned.
Well, Scorpion summoned a hand in UMK3 to kill you. Shinnok did the same thing.
The idea isn't new it was already used in the game. If it were someone's fatality to summon the Dragon King on someone it would take away the originality of that idea.
I posted this idea a few months ago. It's for Nitara: First match one of her fatalities is to vamp her opponent. One of the others is to summon the dead. At first it is just ghosts or something, but after you vamp someone you can summon them in another match to kill your current opponent. And if you vamp sonya and kitana they both are summoned. Maybe when you summon them they vamp your opponent so it keeps pilling up. If that makes any sense...