Here is the full list of all 26 Tunche achievements worth 1,000 gamerscore.
Defeat a boss without taking any damage
Defeat 1000 enemies
Successfully complete one Challenge
Talk with everybody at camp at least once
Buy a Skill
Defeat Mapinguari
Read a Story Chapter of any character
Obtain a Spiritual Core
Enter the jungle
Unlock 30 Compendium entries
Read all four Story Chapters for every character
Reach a SSS Stylish Grade
Buy all Skills for one character
Help all Harvesters fully personalize their camp
Beat all the bosses with each character
Defeat Runapuma
Defeat the Prisoner
Defeat the Final Boss
Successfully complete 20 challenges
Obtain all Spiritual Cores
Beat every type of enemy once
Enter the jungle 50 times
Obtain 500 entropy
Defeat Boutu
Defeat 4 or more enemies with a single Super Attack
Rescue a Harvester