[1.8] Grapling Hook issues, ¿feather spell ¿fly

good days

(broken englis advertisment)

im triying to do a graṕling hook that allow to go down and up from clifs, actually most of the code works but i have and undesired behaveour when the player is hanging form the actualy invisible rope

it begins to bounce up and down erratically, the other ting is im jumping from a 17 blcks tower and the rope is 10 blocks long so when i relese the rope i fall 7 blocks and die like if  jumped from heigther of 17 blocks

so i wass thinking first

lets add to entityes the feather fall spell,  but idont know how

* how do you add the feather speel from code ?

then i think if a made fly the player in this stance in this resting point, bu dont have any idea

* how do you set fly in minecraft ?

then think again  if i create a invisible block in this point for the player to stand

but discarted inmediatly becoze i could shoot downwards

what do you think

thanks for reading