Here is the full list of all 27 Troll and I achievements.
Hunt and skin a boar
Kill an enemy
Craft a melee weapon
Collect 10 health plants
Complete the crash scene in co-op mode
Kill 10 scavengers using spears whilst on Troll's back
Use an explosive spear
Defend against a troll hunter
Use a power stone
A dying hunter tells his story
Drop the aeroplane in the crash scene
Open the troll door and enter the caves
Discover the hide ability
Kill 30 enemies
Kill 60 enemies
Complete the collapsed bridge scene
Complete the mineral mine scene
Defeat the Ahky boss
Free the prisoner
Collect all Troll idols and max out ability points
Collect all Otto idols and max out skill points
Destroy all hunter sirens
Close all fractures
Collect all diary Entries
Defeated Nico and his men
Complete the game in co-op mode
All trophies acquired. Friends for life!