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