This is my guess on what might be part of op ending.Or should i say i just wanna see they fight on the same level.
Somewhere after one piece a spring island on top of not a very high mountain.
Luffy:IAM THE PIRATE KING!!!!
Coby:Luffy the pirate king!!!*claps hand*We totally grow up together didt' we?
Luffy:ahh Coby.No I grew earlier.hahahaha.*luffy poster smile*
Coby:Luffy.U were great but your time is over.I have to put this to an end.
Flashback of the pass appear.All the things the strawhat did.Finding all blue,drawing the map of the world,laboon,
defeat of mihawk,sunny last destination,one piece,message gol d. roger left at the rio poneglyph,rio pneglyph,dragon motives.and finnally the start of OP,Luffy saving Coby from Alvida......
2,3 hours before Coby confronting Luffy.
Coby:Smoker-san?You're badly hurt.Did u stop him?
Smoker:eahhh blackbeard.*faint*Coby just move on.
Helmeppo:Coby blackbeard and luffy is having a confrontation no point of going there now.Lets just wait for the end
let Aokiji go?Kizaru?
Coby:There is no confrontation.Luffy going to defeat blackbeard.But i won't let luffy spread it to the world.
Helmeppo:Spread?butter?we have plenty in the kitchen.You belive the crap Aikainu tell u what OP is about.
Coby:Yes and in absoulute Justice too.
The spring Island.
Blackbeard:Ahh Luffy.*panting*Iam not defeated yet so don't push you're luck!
just let me know what onepiece is!
Luffy:Iam gonna let people know but first.Gomu-gomu no jet giganto pistol!!!!!*punches blackbeard
on his guts*
Blackbeard:*spit out blood*Defeated*I admit defeat.
Luffy:eargh*gomu gomu no jet giganto elephant gun!!!
Blackbeard falls from the cliff.
Usopp:Luffy.Marines battleship is approching this island.We're to exhausted to fight.
Luffy:Tell the others to wait on the ship.I want to ponder for a while.
Sanji:*overheard*Ponder?or u want me to pound your head!Lets go.
Luffy:Ok.but let me shout it out first!!
Luffy and Coby staring in the eyes.
Coby:Now is your time.*soru**punch*
Luffy caught off guard.receive the first blow.
Luffy:*Clear the blood from his mouth*my grandpa teach u well!
Luffy Jumps to the air.
Coby:Did't u fight with the cp9 member luffy.did u forget u lose in the air againts a rokushiki master?
Luffy caught off guard again.remembering lucci's own rokuougan.fall flat to the floor.
Luffy:Smoke coming out from him.seems he activated gear 2nd.Runs toward Coby and punch him.
Coby:Dodge luffy attack.*rankyaku*
Luffy:Earhghh.*panting*I belive iam not fighting seriously.runs towards coby again this time gomu-gomu no jet muchi.
Luffy dodge*jet tsuchi
Coby was sent quite far after receiving jet tsuchi straight to the face.Just about to get up
Luffy:jet pistol follow by jet stamp.jumps up jet twin pistol
Coby suffered heavy damage from receiving multiple blows from luffy.
Luffy panting as he looks at coby:So admiral coby now ehh?you did give me a fight.continue?
Coby:haha?did u really meant it or just want to flatter me?You're tired :and i just arrive.so that question should
be asked by me.Luffy want to continue?
Luffy:You talk like a real marine now.jet bullet.
coby:dodge with soru*genpou*rankyaku*
Luffy:dodge every projectile *gomu gomu no jet pistol
Coby:receive the blow.
Coby:remembered something garp told him.
Luffy:i will end this with.Gomu gomu no jet gigant gatling
coby receiving all the blows.
and fall flat unconcious
Luffy:U shall not pass me just yet coby.not now not until i let the one piece msg out.
Coby just acting unconcious.If this what garp wants.hope garp-san is correct.
this is just my guess and its quite rush.
If it does sucks sorry!