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