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.
Complete all pursuit courses.
Unlock all courses in School.
Complete all courses.
Complete a course with Buddy.
Lose Buddy to the lava.
Get a basketball into the hoop in Playground.
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.
Unlock a follower.
Unlock all courses in Basement.
Complete all Pogo trials.
Complete all Tiny Toy trials.
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.
Complete all courses and trials in School.
Unlock all courses in Playground.
Complete all courses and trials in Playground.
Complete the Intro.
Complete the first course in Tutorial.
Jump 100 times.
Jump 1000 Times.
Jump 5000 Times.
Perform a "late" jump right after leaving a ledge 77 times.
Complete a course with no deaths.
Complete a Pogo trial.
Complete a Tiny Toy trial.
Build up boost to 5 m/s.
Complete your first "pursuit" course.
Complete all challenges for a single course.
Unlock your first character.
Unlock all courses in Tutorial.
Complete all courses and trials in Tutorial.
Tweak something in the Options menu.
Die by Collision.