Here is the full list of all 9 ChestMate Playtest achievements.
Finish 10 levels in storm mode
Finish 10 levels in storm and classic mode with all your score
Finish 10 levels
Kill a pink starfish with a green short
Kill a five eyes jellyfish
Kill 10 enemies with one explosive barrel
Kill 100 skeletons
Kill 2 enemies with one cannon ball
Finish the first level