Here is the full list of all 43 TRI: Of Friendship and Madness achievements.
Create the biggest triangle possible.
Complete TRI.
Reflected one single light ray 50 times.
Beat "Overcoming Limitations" without collecting the TRI artifact.
Play through Chapter 14 and 15.
Find all hidden idols in 14 levels.
Find one of the two super secret idols in "Out of Space and Time".
Find one of the two super secret idols in "Prisons".
Play through Chapter 12 and 13.
Find the super secret idol in "Going Astray".
Find the super secret idol in "Out of the Box".
Play through Chapter 9 to 11.
Find one of the two super secret idols in "Red Means Dangerous".
Laser yourself to death ten times.
Find one of the two super secret idols in "Interrupting and Bending".
Fall into deadly acid pits ten times.
Find one of the two super secret idols in "Glimpse of Light".
Play through Chapter 5 to 8.
Find all hidden idols in seven levels.
Find the super secret idol in "Wings in the Void".
Find one of the two super secret idols in "Unwilling Walls".
Find one of the two super secret idols in "The Foxes' Playground".
Create 1,000 triangles.
Find one of the three super secret idols in "Overcoming Limitations".
Find all hidden idols in three levels.
Find one of the two super secret idols in "Three Sides to Everything".
Find one of the two super secret idols in "Tower of Nowhere".
Find all hidden idols in one level.
Find one of the two super secret idols in "The Odd Gods' Entrance".
Play through the first four Chapters.
Play through the tutorial mission.