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.
Unlock all courses in School.
Complete all Tiny Toy trials.
Complete all pursuit courses.
Complete all courses and trials in Basement.
Complete all courses.
Unlock all courses in Basement.
Complete all Pogo trials.
Complete a community map course.
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.
Pick up a pair of scissors and run with it.
Pick up a knapsack and run with it.
Complete a course with Buddy.
Lose Buddy to the lava.
Use a water fountain.
Get a basketball into the hoop in Playground.
Complete all courses and trials in School.
Complete all courses and trials in Playground.
Unlock all courses in Playground.
Complete your first "pursuit" course.
Unlock all courses in Tutorial.
Complete all courses and trials in Tutorial.
Jump 5000 Times.
Complete the Intro.
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.
Complete a Pogo trial.
Complete a Tiny Toy trial.
Build up boost to 5 m/s.
Complete all challenges for a single course.
Unlock your first character.
Tweak something in the Options menu.
Die by Collision.