I'm only counting the guest characters who aren't originally part of the Mk Lore, so characters like Skarlet, Sindel or Nightwolf don't count leading up RoboCop

9. Leatherface

8. Freddy Krueger

7. Predator

6. Alien

5. Joker

4. Jason

3. Terminator

2. Kratos

1. Spawn