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