I feel like Luffy will fight Decken soon, so I thought I would throw in my take on the fight. As a side note, if you aren't laughing, hopefully in hysterics, then I have failed. Yeah, it's going to be that kind of fight.
Jinbe finishes his story, and the group starts to make plans to counterattack. While they are doing this, Vander Decken IX comes flying in on a rock.
Decken: Shirahoshi! Baby, I can change!
Shirahoshi: No, go away!
Luffy: Jinbe, I got the rider if you got the rock!
Jinbe (rolling up his sleeves): Way ahead of you.
He jumps up and shatters the rock, everyone scatters as the pieces rain down, with Decken still flying.
Luffy: Gomu Gomu no Pistol!
He hits Decken square in the face, knocking him to the ground.
Decken: You again? Fine, if you're going to stand in the way between me and Shirahoshi, then I'll fight you for her! I challenge you to fisticuffs! The winner gets to marry the princess.
Luffy (talking to Shirahoshi): Don't worry, he's not so tough.
Decken: Were you listening at all!?
Luffy: No, but I'm not going to let you have her!
Decken (smirking): By the way, I don't think we've been introduced. I'm Vander Decken.
Luffy: I'm Luffy.
Decken (extending his left hand): Nice to meet you.
Luffy (goes to shake it): I guess...
Hatchan (from a distance): Luffy, don't let him touch you!
Decken: Bahohohoh! You just made your defeat all the easier for me!
Luffy: Whatever. Gomu Gomu no Bazooka!
He hits Decken and sends him flying.
Luffy (running after him): Gomu Gomu no Gigant Stamp!
His enlarged foot pounds Decken into the ground.
Luffy: Is that all you got? I thought stalkers were supposed to be strong.
Everyone: WHERE DID YOU HEAR THAT!?
Decken (getting up): Not by any means.
From out of nowhere he pulls out three large hammers
Decken: Let's see if you can handle my power!
He throws his hammers behind him, one at a time.
Luffy: Huh? Your aim is not very good.
Decken: That's not what Hatchan said!
Luffy: So you're the one who did this to Hatchan.
The hammers fly toward him.
Luffy (enlarging his fist): Gomu Gomu no Oh Hell No! Gomu Gomu no Bitch Please!
He swats away the first two, but the last one skips him and heads for Shirahoshi.
Luffy (jumps in front of Shirahoshi): Gomu Gomu no Bumper!
His body widens, but stays thin as a piece of paper. The hammer is sent back at Decken.
Decken: Little help here!
A giant hand comes from beyond the forest. It's Wadatsumi.
Wadatsumi: I got it boss.
Sanji and Chopper: Oh hell no!!
Sanji: Diable Veau Shoot!
Chopper: Kung Fu Point!
Sanji lands his kick on Wadatsumi's face, while Chopper attacks his hand, making him pull it back.
Wadatsumi: OW! That hurt. :(
Chopper: NO! Bad umibozu! Now walk it off and apologize to us for trying to hurt our friend, and to yourself for getting your ass handed...to yourself!
Sanji: Luffy, we got umibozo the clown here under control. Focus on your fight.
Luffy: Ok. Buggy might be pissed you stole his epithet, but that's beside the point. Back to you, creepy!
Decken: I see your crew is strong. Let's see how you like this!
He throws an odd looking metal ball at Luffy.
Luffy: Again, 'the hell? Gomu Gomu no Clothesline!
He catches the ball with his fist and it explodes on impact.
Luffy: Ow, you burned my arm. Prepare to die!
Decken (throwing a second bomb): Have another!
Luffy: Gomu Gomu no Rebound!
The bomb bounces off his stomach and explodes in the air.
Decken (takes out a bazooka and loads a few rounds): I'm not done!
Sanji: Really? Cuz I just put a meat thermometer in you and it says you are.
Decken: When the hell did you have time to stab me in the arm!?
Sanji: When you were getting your ass kicked.
Luffy grabs Decken's feet.
Luffy: A giant mechanical bear once asked me "If you were to go on a trip, where would you like to go?" I now pose the same question to you.
Decken: To the depths of Shirahoshi's heart so she can realize our love.
Luffy: How about hell?
Decken: No wait! I changed my mind. I want to go to Disneyland!
Luffy: No, you're going to a watery hell! Franky point to where The Underworld of the Sea is!
Franky: This weeks trajectory says... (points) there!
Luffy: Enjoy hell. Gomu Gomu no...
Decken: Screw you, I'm going to Disney...
Luffy: ROCKET LAUNCHER!
Decken flies off toward The Underworld of the Sea.
Luffy: Shirahoshi, think about your mother and the Underworld at the same time and yell.
Shirahoshi: But what will...?
Luffy: Just do it!
Luffy: Decken should have some fun now.
Luffy: Don't worry, crybaby, he won't bother you anymore.
Shirahoshi: Luffy, about what Decken said earlier...
Luffy: What about it?
Nami: You weren't listening when Decken said what the winner would get, were you?
Luffy: Nope. What is it? I hope it's meat!
Nami: You never pay attention to what others say, do you?
Luffy: Nami, what are you talking about? Why does Sanji look furious? And why is everyone giving me awkward looks? Can we kick Hordy's ass yet?
Den: Yes, Luffy. Let's kick his ass.
And the group sets out to Ryugu Palace, Luffy none the wiser.