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 course with Buddy.
Lose Buddy to the lava.
Unlock a follower.
Complete one sticker set.
Pick up a pair of scissors and run with it.
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.
Complete all courses and trials in Master Class.
Unlock all courses in Master Class.
Complete all courses and trials in Wholesale.
Find the hidden fort in Wholesale.
Unlock all courses 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.
Pick up a knapsack and run with it.
Use a water fountain.
Complete all challenges for a single course.
Die by Collision.
Complete your first "pursuit" course.
Complete all courses and trials in Tutorial.
Unlock all courses 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.
Build up boost to 5 m/s.
Get a basketball into the hoop in Playground.
Complete a course with no deaths.
Unlock your first character.
Complete the first course in Tutorial.
Jump 100 times.
Complete the Intro.
Tweak something in the Options menu.