Here is the full list of all 11 Shield Cat Playtest achievements.
Start a new game of Shield Cat.
Collect all Fish Scales in a single stage.
Collect all LANCE Letters in a single stage.
Collect all Cat Coins in a single stage.
Defeat the Big Mushroom in the Lignum Woods.
Collect one Fish Statue.
Fill out the entirety of the map in a single stage.
Beat River Challenge 1 while getting all stars.
Complete a Marcus' Adventure challenge while collecting all the crystals.
Complete a hard Marcus' Adventure challenge while collecting all the crystals.
Complete a Red Gem challenge.