Ok - for know I tried to sort out any issue about my null-objects, sprite cropping and collision polygons. There for I did the following:
When I make all frames dimension the same (sprite editor - resize - 350 x 350 center mid), set every animation and all their frames collision box to bounding box and give all animations/their frames the same null object position, everything works superb perfect!
But as soon as I start the last tweaking, customising the collision boxes, my animations go craaaaazy
EDIT:
I think I understand the problem. If the collision boxes height of the "idle" animation is less then the "fall" one PLUS both having the same null point position, it causes the glitch (fall hits ground - changes to idle - but idle is "shorter" and falls, creating a loop and glitching between the two)
But I thought if I rise the null position the same amount i raised the bounding box, it should fix it but its not. Am I thinking wrong there somewhere?