Yep, and sometimes you can uppercut them straight into the Pit before the final round is over. I think they have to be in Danger, or enough so an uppercut kills, and perhaps they might have to be in the air when you hit them also - I can't remember exactly.

If you get it, when they land in the Pit the floor is higher and there's some weird blue area underneath:



First time I did it, the next opponent on the Pit Bottom was - Reptile! Which was kinda cool.

thats what sub zero did to me in mk 2. i was in danger, he did the ultra freeze then he uppercutted half my body into the dead pool