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