Here is the full list of all 38 Platypus Adventures achievements.
Equip the backpack
Equip the Boomerang
Obtain a new backpack
Get a warm meal cooked for you
Take a nap in a rest area
Put on a hat
Walk along the bottom of a creek
Use a Zipline
Knock a Quandong berry down from a tree
Smash open a Pumpkin
Take a ride on the back of a Cassowary
Ride a wave in the ocean
Win a match of Melonball
Smash open a Coconut
Collect a Pearl from inside a Clam
Swim closely to a Humpback Whale
Use a Seashell with a piece of the Meteorite
Swim closely to the Giant Squid
Purchase an item from the vendor at Kurlibul Coast
Construct a bird bath for the Seagulls
Obtain the Ocean Armour
Cut down the special vine for Koala
Experience a close encounter with the Entities
Collect a Bush Tomato from a bush
Knock a Macadamia Nut down from a tree
Do a jump off the ground while you are sliding down a sandy slope
Obtain the Cactus Bludgener
Trade some Bush Tomatoes for Coconut with Emu
Deal damage to an opponent while you are sliding down a sandy slope
Deal damage to an oppenent by guiding them into a Cactus
Travel to the Secret Swimming Hole, at Boondaburra Forest
Travel to Barnancle cave, at Kurlibul Coast
Travel to Sandy Lookout, at Karratha Desert
Open the Encyclopedia
Complete the campaign while wearing a hat
Complete the campaign on Hard
Complete the campaign on Extreme
Open the door in the ancient temple