Imagine Optimus Prima and Captain Kirk facing off against Scorpion and Sub-zero?
Of course, it's ridiculous, but is Robocop doing a front flip any more absurd? Imagine human-sized Optimus Prime getting fried into a human skeleton by Scorpion or having his intestines ripped out. :P If he gets killed by Megatonr (another guest character), there's an exclusive fatality where it just runs the video footage of his death from the 1986 animated filml.
Also, Captian Kirk has a fatality where he beams the opponent into the Enterprise as it's self-destructing (Trekkies will get this one). He can use his phaser and throw tribbles to stun the opponent.
Yeah...this is more of a critique of the ridiculous guest characters we've been getting. I'm half-expecting Alf and Johnny 5 to be announced next.
BTW...why hasn't Ed Boon ever guest starred in MK? His friendship could be a bunch of women showing up. (old schoolers may get this joke).