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