Here is the full list of all 53 Hidden Cats in Spooky Town achievements. It takes around 1-2 hours to unlock all of the achievements on Windows.
You Found Stella
After Party Completed
You Found 700 Cats
You Found 600 Cats
You Found Marrie
You Found The Vampire Cat
You Found Camarguinho
You Found The Mummy Cat
You Found The Cat Noir
You Found 500 Cats
You Found The Pumpkin Cat
You Found The Witch Cat
You Found Satanas
You Found Barbie
Graveyard Completed
You Found 400 Cats
Pumpkin Theme Completed
You Found 300 Cats
You Found 250 Cats
Vampire's Lair Completed
You Found 200 Cats
Witch's Cabin Completed
You Found 150 Cats
You Found 110 Cats
Found All Cats Normal
Finish with no Hints Normal
Mad Doctor's Lab Completed
You Found 100 Cats
You Found 95 Cats
You Found 90 Cats
You Found 85 Cats
You Found 80 Cats
You Found 75 Cats
You Found 70 Cats
You Found 65 Cats
You Found 60 Cats
You Found 55 Cats
Ghost House Completed
You Found 50 Cats
You Found 45 Cats
You Found 40 Cats
You Found 35 Cats
You Found 30 Cats
You Found 25 Cats
You Found 20 Cats
You Found 15 Cats
You Found 10 Cats
You Found 5 Cats
Finish with no Hints Advanced
Found All Cats Advanced
You Found Pandora
You Found Pretinha
You Found 800 Cats