DrahminTo obtain Drahmin, the Oni-Tormentor of the Netherealm, simply succeed in a Tag Team Tournament on the "Normal" difficulty. You may lose an infinate amount of times.
To acquire Hsu Hao, the Red Dragon assassin and thief, simply obtain victory in a Tournament in the "Normal" difficulty. You may lose an infinate amount of times.
Reptile, the Zatterian genocidal murdering raptor, can be unlocked by completing "Arcade" mode of Tournament Edition with all Kombatants under the difficulty of either "Normal", "Hard", or "Very Hard".
Sektor, the traitor to the Lin Kuei clan following the mechanisation during and leading to the era of Mortal Kombat 3 and Shao Kahn's invasions, can be unlocked by completing a "Tag Team" tournament on "hard" difficulty without failing. You may need to do this twice, as it can also unlock other fighters. Sektor had apparently fled to Japan to begin a clan of his own mechanised cyborgs and had murdered the previous Lin Kuei grandmaster who had him shifted. Sektor is a very powerful fighter who is one of the strongest fighters in MK: Tournament Edition.
Noob Saibot, the former-Brothers of the Shadow demon assassin, can be unlocked by completing Tournament Edition with all Kombatants under the "Hard" or "Very Hard" difficulty in both "Arcade" and "Tag Team" mode. After completing that task, win the Tournament in Arcade mode using Scorpion's alternate, "Smoke Scorpion", a pallet unlocked in Koffin EF. Another method for the former process is to beat the game with "Repear Scorpion", which can be unlocked in Koffin FN. Upon doing this, the mysterious demon, who was thought dead upon the failure and subsequent death of Shinnok at the hands of Quan Chi.