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