I've been playing a bunch of Mortal Kombat the past couple of days and every once in a while I'll get a glimpse of characters in the background that aren't in the game but are obviously ones from earlier games. I will see Frost fighting on a bridge in the background for example, has anyone else seen characters that aren't in the game but are clearly from past games.

Tanya from MK 4, is tied up in the coliseum background, along with may be the dlc girl scarlet or whatever her name was but im not sure, could be a random model they had laying around

Yeah it's fun to look out for these things, if you see Smoke peeking out behind the Living Forest stage, thats how you can engage him in one of the secret fight achievements, if you press down + Start as he peeks out beside one of the trees...

Tanya and Skarlett can all be seen as prisoners on Kahn's arena.  Li Mei and Sareena were one of Kahn's prisoners before, but i havent seen her in the official release.  Rain was also seen in the cathedral as the one dissecting the body before the official release, but he hasn't shown up since the full release either.  So he, Li Mei and Sareena were probably just placeholders before the official release.

Sareena & Reiko are also fighting in the pit background. As is Daegon, but he took me awhile to figure out. No idea why. He's such a memorable character.