Hey,

To unlock all four achievements you will have to do two playthroughs.

- After finishing the first playthrough you will get the 'regular ending' and unlock the 'Give me my jumps back!' achievement (try to finish this playthrough with at least 30 jumps left; that will unlock three extra challenges).

- During the second playthrough you will collect all 6 medals- 'Explorer frog' achievement- and at the end of that playthrough you will also unlock the 'BONK' achievement. (Please note that after a medal is collected, it's yours forever, even after you restart, so no need to go for it again!)

- Finally, there are 4 extra challenges. Upon completing those you will unlock the 'Completionist frog' achievement.

Timestamps:

0:25 First playthrough

3:02 Second playthrough
3:30 Medal 1
3:59 Medal 2
4:36 Medal 3
5:04 Medal 4
(at 5:12 restart and then replay to that level with water at 5:16)
7:56 Medal 5
(at 8:41 make sure to grab a couple fireflies so you can see in the dark)
9:33 Medal 6

12:04 Challenge 1
12:27 Challenge 2
13:01 Challenge 3
13:38 Challenge 4

EDIT: After making the video I discovered that it's possible to save one more jump. In the video at 1:58 it's possible to jump between the spikes there, under those three falling blocks. But it's super precise and I wouldn't recommend going for it.

EDIT 2: You can actually save 2 jumps there and much easier. Make the first two blocks fall and then just walk off to the right from that second block- you should go between the spikes. (Thank you Zepy for this info!)

If you have any questions, suggestions, criticisms, found any mistakes and so on, please let me know!

Thanks to the developers for making a good game and thank you for checking out my guide!