the last level is incredibly easy, i only used 2 items i'll describe is as best as i can: put the first board on the tip of the board on the edge, then tack on the other board on the second board as it falls, between the top of the box's head and the platform above him
the reason ppl cant get double jump to work all the time is because they go too far off the edge (falling off counts as a jump) then they double jump when there falling, so start your jump sooner also, if you spin, you already double jumped.
level 9 on world 1, maxed hp mp and last guardian. 2/5 would like to see level caps on games like this, unstead of being able to just grind through the easiest level.