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