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