I just wanted to share a pretty good video that allowed me to make instant progress.
I work on both version of butterfly, a long one as displayed by some swimmers and the standard take on butterfly trying to find someting that fits me.
In the latter I could not get my pelvis up, I could force it up but it was feeling neither right or efficient. The vid fixed this for me by creating proper timing betwen my upper and lower body motion.
You guys can subscribe to his channel it may motivate him to do more vid (youtube revenues are all about subscribers count).
PS, for the ref I'm not affiliated to him in anyway.