There are 12 animal types to kill. Most you can find them on the key of your world map:
Animal/Where to findBlack and White Tiger - Island/World Map
Devil Goat - Island/World Map
Mutant Boar - Island/World Map
Cyber Panther - Island/World Map
Cyber Shark - Island/World Map
Mutant Buffalo - Island/World Map
Mutated Cassowary - Island/World Map
Robo Dog - Several missions and garrisons have these
Blood Dragon - Required for several other achievements/story progression
Mutated Turtles - Required for a hunting side mission
Robo Crocodile - In the same hunting mission, you'll be attacked by one
Neon Snake -
These don't appear on the world map. My first suggestion is to play the game naturally, I ran into 3 (including one glowing white in the water). If you're done with everything then here is a good place to look:
Fast travel to the garrison in the NW corner of the map.
Travel south out of the garrison, and check either of these two places:
Down the hill about half wayor
At the base of the hill at the roadIf you don't see them (or if there's a dragon, that seems to affect it). Run a couple hundred meters away or try fast traveling back and forth until it spawns. I duplicated this many times.