Andreux,
Yes, Reptile was in MK 1. It was a secret, and you scored 1 million points if you found him and defeated him.
On the pit stage, I believe (it’s been a long time) you have to get a double flawless victory AND do the Pit fatality (knock the opponent into the pit).
Then Reptile comes out and you fight him IN the pit.
BTW, if you get the special edition of Mortal Kombat Deception for Xbox, it comes with an ‘arcade perfect’ version of MK1.