METAL SLUG 3

Here are all the Slug locations, variant color versions don't count, but there are 11 of them to find and ride. Just simply jump onto them and it counts as riding them.

Metal Slug/Gold MS - Gold MS if you take Mission 1's boat path, will be available to ride before boss fight. Regular MS drops in mission 5 in the spaceship area fighting clones of your kidnapped character. Also automatically boards the Regular MS before fighting "Rootmars" (Final Boss).

Camel Slug - Start of Mission 4

Slugnoid - If you reached then exit of the top or bottom areas of mission 1, it will be there before the boss fight (in red color), also in Mission 5 in the last area (where you fight the zombie clones, in brown color).

Elephant Slug - Way at the end of the "Iceman" Cave on Mission 2.

Ostrich Slug - Mission 3 top path

Rebel Armor - Mission 3 straight and bottom path, also in Mission 5's last area.

Drill Slug - Mission 4 bottom path (with the many insects and crabs there.)

Astro Slug - Automatically boarded after you take down Fake Morden in Mission 5 (a "Mars People" in disguise.)

Slug Mariner - Mission 1 bottom path, can't miss it, viewable in plain sight. Also in Mission 3 bottom path.

Slug Flyer - Mission 5 at start, there is a choice of 2 slugs, take the one that's plane shaped.

Slug Copter - Mission 5 at start there is a choice of 2 slugs, take the one that has rotor blades on top, also on next area if you choose to not board a vehicle or if your vehicle is already gone.