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