Hello friend, thank you for the comment!
To make the double jump, you need to transform in the yellow monster and then you do a normal jump and while in the air you need to press the action button "z" or "j". This way you're to make double jump!
If you need help again feel free for commenting here or sending me an email:
diel.mormac@gmail.com
Kind regards,
Diel Mormac