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.
Unlock a follower.
Complete one sticker set.
Complete all Tiny Toy trials.
Complete all Pogo trials.
Complete a course with Buddy.
Complete all courses and trials in Master Class.
Unlock all courses in Master Class.
Find the hidden fort in Wholesale.
Complete all courses and trials in Wholesale.
Unlock all courses in Wholesale.
Use a water fountain.
Unlock all courses in School.
Complete all courses and trials in School.
Lose Buddy to the lava.
Complete all courses and trials in Playground.
Unlock all courses in Playground.
Jump 5000 Times.
Die by Collision.
Get a basketball into the hoop in Playground.
Pick up a pair of scissors and run with it.
Pick up a knapsack and run with it.
Complete all courses and trials in Tutorial.
Complete your first "pursuit" course.
Unlock all courses in Tutorial.
Build up boost to 5 m/s.
Complete a Pogo trial.
Complete a Tiny Toy trial.
Jump 1000 Times.
Perform a "late" jump right after leaving a ledge 77 times.
Complete all challenges for a single course.
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.