The new pets
The fine folks at Petopia have a thread collecting all the info on the new pets, which is where this info on the new rare spawns comes from, including screenshots of what each type of track looks like (from the delightful Kalliope).
Note that we don't know yet if these are the final skins for the beasts. There is also supposed to be a rare silkworm and spirit beasts that at the time of this writing have not yet been found are going to be available in patch 5.1.
You can find maps of the paths of several of the rare spawns at the Why? Because it's Rare! blog.
Tracks: Bloody tracks
Location: Jade Forest central forest near Serpent's Heart
Family: Water strider (exotic)
Tracks: Flooded tracks
Location: Jade Forest central area near Temple of the Jade Serpent
Tracks: Barely visible tracks
Location: Valley of the Four Winds west-central, from Halfhill to Stoneplow
Tracks: Muddy tracks
Location: Krasarang Wilds, islands in the south
Rockhide the Immovable
Tracks: Worn tracks
Location: Townlong Steppes, central area south of Fire Camp Osul
Tracks: Puzzling tracks
Location: Kun-Lai Summit southern area around the Yaungol Advance
Tracks: Heavy tracks
Location: Kun-Lai Summit in the mountains through Mount Neverest
Family: Water Strider (exotic)
Tracks: Mysterious tracks
Location: Dread Waters around the perimeter, around the Stinging Trail
Family: Quilen (exotic)
Tracks: Dusty tracks
Location: Vale of Eternal Blossoms central zone, often near the Mogu'Shan Palace
Spawns in four different colors.
The long, slow slog
I should point out that as cool as this concept is, finding the pets is going to be a bit difficult. If you thought finding spirit beasts was tough, try finding tiny footprints that may be somewhere on the ground -- or maybe floating a bit over the ground or under the ground. (Hopefully, most of those issues will be fixed before it goes live.)
I can say from my experience that as fun as following the tracks can be, finding those tracks in the first place can be a challenge. Currently in the beta, the respawn rate has been sped up, and we can only assume that the spawn rate on live will be somewhat similar to spirit beasts.
I suspect that if you happen to stumble across some tracks while out in the world, it will be an exciting adventure and bit of stalking. But if instead you decide to seek out one of the rare spawns and find yourself endlessly creeping around the land, looking for tiny tracks and cringing every time you see another hunter for fear that they're -- well, that's probably going to be a certain level of frustrating.
One tip from Petopia that is very helpful is to turn down your ground clutter as far as possible to make it easier to spot the tracks.
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