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