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