In the original Mortal Kombat game released in 1992, there aren't any playable secret characters available to be unlocked. The concept of secret characters as playable options was introduced in later Mortal Kombat games. However, the first game did include a secret fighter known as Reptile, who served as an unplayable hidden opponent. You could encounter Reptile by meeting a set of specific conditions in the game: 1. You had to be fighting on The Pit stage, which is recognizable by the bridge above a pit of spikes. 2. Something had to fly in front of the moon on the game screen, which occurs at random. This was usually a silhouette of Santa Claus in his sleigh or a witch on a broom. 3. You had to achieve a Double Flawless Victory, which means you needed to win both rounds without taking any damage yourself. 4. You had to execute a Fatality at the end of the match without using the Block button at all in the final round. If all these conditions were met, you would be taken to the bottom of The Pit, where you would face Reptile as a hidden boss. He had the combined powers of both Scorpion and Sub-Zero, making him a formidable opponent. It's important to note that while Reptile was a teaser for future secret characters to come, he was not a playable character in this game. In subsequent Mortal Kombat titles, additional secret characters were often included, and many of them were unlockable or playable after fulfilling certain game conditions. The challenge and allure of discovering these hidden fighters became a hallmark of the Mortal Kombat series, contributing to its lasting popularity and intrigue among fans.