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