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