Here is the full list of all 41 Hot Lava achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Complete a community map course.
Complete a course with Buddy.
Lose Buddy to the lava.
Find the hidden fort in Wholesale.
Unlock a follower.
Complete one sticker set.
Complete all pursuit courses.
Complete all courses and trials in Wholesale.
Complete all courses.
Complete all Pogo trials.
Unlock all courses in Wholesale.
Pick up a knapsack and run with it.
Pick up a pair of scissors and run with it.
Use a water fountain.
Complete all courses and trials in Basement.
Complete all courses and trials in Master Class.
Unlock all courses in School.
Complete all courses and trials in Playground.
Unlock all courses in Basement.
Complete all Tiny Toy trials.
Jump 5000 Times.
Unlock all courses in Master Class.
Unlock all courses in Playground.
Complete all courses and trials in School.
Tweak something in the Options menu.
Complete a Pogo trial.
Complete all courses and trials in Tutorial.
Jump 1000 Times.
Complete all challenges for a single course.
Get a basketball into the hoop in Playground.
Die by Collision.
Complete a course with no deaths.
Complete your first "pursuit" course.
Unlock all courses in Tutorial.
Complete a Tiny Toy trial.
Perform a "late" jump right after leaving a ledge 77 times.
Build up boost to 5 m/s.
Jump 100 times.
Complete the first course in Tutorial.
Unlock your first character.
Complete the Intro.