Here is the full list of all 35 SAMUDRA achievements.
Find the Developer Room
Start Chapter 5
Get inside the Prehistoric Shark in Whale Belly
Collected 50% Trash
Start Chapter 4
Save 2 Puffer
Receiving the lantern for a 2nd time
Start Chapter 3
Find the hero in a box easter egg
Start Chapter 2
Death 20x
Save 1 Puffer
Find the Pilot cave in Coral Grave
Pet 1 Sea Bunny
Start Chapter 1
Find the Wall Painting in the Prologue
Collected 1 Trash
Receiving the Lantern for the 1st time
Start the Prologue
Clear the game
Death by pitfall 5x
Zero death during all chase sequences
Speak to Hobopus 20x
Listen to a full song loop by Hobopus
Choose The Fish
Choose The Machine
Try both endings
Find the Helm Grave in Oil Rig
Find the Sea Bunny room in Oil Rig
Find the Secret Temple in Stone Cave
Find the Chemical Room in Sunken City
Collected 100% Trash
Save 3 Puffer
Save 4 Puffer
Save 5 Puffer