Oddworld: New 'n' Tasty

There are actually at least 16 ways you can kill a Slig in the game.
The 15 I used are

1) Electric Shock - Walk one into any Electric Fence
2. Hand Grenade - Cooked or otherwise, doesn't matter
3. Ground Mine (Static) - The mines which don't move / beep
4. Switch Mine - The mines which you can de-activate with the right timing
5. Air Mine
6. Timed Mine
7. Falling Rock - Pull a lever to drop a rock on a Slig
8. Falling Meat - Pull a lever to drop a chunk of meat on a Slig
9. Shot - Shoot a Slig with another possessed Slig
10. Blades - There are a few places you can pull a lever to drop blades onto a Slig
11. Slog - Slig... meet Slog
12. Chant - Chant for a second time to blow up your possessed Slig
13. Trapdoor
14. Shrykull - Obtained later on in the game
15. Rupture Farms Grinder - Not to be confused with the blades, you need to have one fall into the grinder blades in the floor in Rupture Farms for this one.

There are 18 ways to kill a Slig. You only need to complete 15 for this Trophy. One of these 18 ways is to complete the game with more than 150 Mudokon's rescued.

Make sure you attempt this Trophy in one Story run and not through Chapter select.

You can find the Timeline in the Youtube Description to find specific Kills.