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