I wanted to wait until the tournament was over before writing this, but I couldn't keep myself. The current situation in the manga has presented me with an opportunity to write something I've wanted to do, and have been working on for a long time. It should be good. I used the finishing moves from my last fight predictions with Nami and Brook, just as a means for comparison. I may take advantage of plot convenience to set things up right, but nothing too horrible. Anyway, enjoy.
Nami and Usopp are guarding the kids when they see Slime.
Nami: What is that thing?
Usopp: I don't know, but I think you should check it out.
Nami: Coward. If anything happens to these kids while I'm gone, you're as good as dead.
Nami runs off.
Meanwhile, Sanji and co. have made it to where the others are.
Brook: What is that thing? It's my opposite. I'm all bones and no skin, it's all skin and no bones!
Luffy: So, what am I supposed to do with this guy?
Smoker: Hand him over!
Franky: Wait a damn minute!
Nami runs in.
Nami: What is that thing!?
Clown: I keep telling you, it's Slime, the accident 4 yea-
Luffy: So how do we beat this thing if we can't punch it or blow it up?
Zoro, Brook, and Sanji arrive just then.
Zoro: He doesn't look friendly.
Luffy: You guys don't worry about that.
Law appears via his power
Law: Luffy you idiot! I told you not to just charge in! You have him? Good. You, Zoro, and Sanji are coming with me, and bring him with us.
Luffy: Before you do that, send Smokey, the Marines, and the centaurs to a part of the island where they'll be safe from that thing.
Law: Fine (he uses his power, they all disappear). Now we go.
Nami: Freeze, creepo! You aren't going anywhere until you put me back in my own body!
Law: Oh yeah, I almost forgot. Shambles!
Nami and Sanji switch bodies.
He uses Room again and all five of them, and Kinemon disappear.
Nami (looking up at Slime): Robin, go see who's still inside. I got this.
Brook: Franky: Go see who else is inside. I got this.
They both go inside. Nami and Brook are left to size up the gelatinous behemoth that stands before them.
Nami: Any ideas? Burning and touching are both off the table.
Brook: Hit'em with all we got and see what works.
Nami (pulling out her Clima-Tact): Works for me.
Brook: These cold lands do wonders for my soul. And what's good for the soul is good for the sword. Try this! Waltzing Machillda.
He starts running around Slime, doing pirouettes at regular intervals, sending a cold wave at Slime each time. The ice holds on Slime, but only covers a small fraction overall.
Slime: Bleep bloop.
He swats the ice away.
Nami: My turn. Thunderbolt Tempo!
The lightning hits Slime's recently grown arm, and slices it clean off.
Nami: That's how you take down a....whatever that is.
Her rejoice is shortlived, as the arm merges back with the rest of the creature.
Brook: It can regenerate. This isn't good. What do we do now?
Nami: We keep hitting it until we get something that works!
Slime is now on the offensive, pulling out chunks of his body and hurling them at Nami and Brook. They start dodging.
Brook: There's too many! We can't counter!
Due to all the globs it's thrown, there is now a large hole in Slime's midsection.
Brook: Run toward it! Maybe we can hit its insides.
They start running, but get only a few steps.
Nami turns around to see her friend has tripped, one of the blobs from earlier pinned his ankle as it moved back to Slime.
Nami: Hold your breath and don't move!
She waits until the Slime passes over Brook then runs to him.
Nami: Are you okay?
Brook: I think so. Good thing I have no skin, or else that would have burned. We need to be careful and watch our backs for those things.
Nami: You're right. Listen, I've been thinking, we need to think bigger with our attacks.
Brook: I agree. But what do we do?
Nami: Let's see if we can cut it down to size. (she runs at it) Bolt Whip!
A rope-like bolt of lightning comes out of the end of her staff, cutting off a part of Slime's head.
Brook: Fubuki Giri!
They manage to separate and freeze the detached chunk.
Nami: 1 down, so many to go.
Slime simply picks up the frozen section and melts the ice using the acidity of his hand.
Brook: Oh, not again!
Nami: Brook, I'm going to try and get a storm going, so I need you to distract him.
Brook: Consider it done.
Brook: Hey, ugly! I would call you boneheaded, but that would be an insult to people with bones! Icecapadian Slash!
He launches a circular wave at Slime. It goes through its body, leaving a clean circle where it cut through, like a cookie cutter.
Slime: Brrrrrrrr (but more grunty).
Slime takes his hand and tries to slam Brook.
He spins his sword over his head, drilling through Slime's hand as it came down. There is a small amount of ice around the rim of the hole, but it doesn't do anything.
Slime now sets his sights on Nami, distracted by her storm, and moves in her direction.
Brook (realizing what the thing's trying to do): Oh no you don't! White Winter's Suite: Gusto Harmonia Rondo!
He jumps between Slime and Nami, conjuring a cold wind using his sword's power, knocking Slime back.
Nami: Hey, fatty! Catch! She throws a magnet at Slime, and to her delight it gets caught in its belly.
Brook: Nami, won't that corrode? And how's the storm coming?
Nami: Great, and I want it to. That's a special metal that retains its magnetism regardless of its physical state. I just turned that thing into a huge, jiggly lightning rod. Now, where was I? Oh right, JUDGMENT OF ERASMUS!
A giant ball of plasma (ie lightning) descends from the clouds created by the storm, right over Slime.
Slime looks up and sees it. He opens his mouth, and eats it.
Nami: WHAT THE HELL!? THAT'S NOT SUPPOSED TO HAPPEN!
Brook: That thing just ate a ball of pure lightning. What are we dealing with here?
A rumbling sound is heard from Slime.
Nami: We need to find cover. There's about to be huge electrical interference!
Nami: Just duck! This is bad. I should have realized this. Why'd that thing have to eat my lightning?
Brook: Care to explain?
Nami: Well, it's electricity that interacts with a magnet which is then released in wave form. Couple that with the sound waves generated from that thing and you've got a COMPLETE FUCKING DISASTER! I just turned that thing into a giant electro-magnetic pu-
There is a shockwave, and weird noises are heard by the lab.
Nami: -lse cannon.
Brook: Oh. Hey, Nami, what say we try a combination attack, since my cold and your lightning seem to accomplish our task partly.
Nami: How will that work?
Brook: Now it's my turn to conjure a storm.
He waves his sword like a conductor prepping an orchestra for a downbeat.
Brook: Niveo Melodium!
A small snow storm forms around him and Nami.
Brook: Now, on my signal, combine your electricity with my wind. Staccato Gale! NOW!
Nami puts the tip of her staff just after the end of Brook's sword, and electricity flows through it, the combo attack hitting Slime squarely in the chest, paralyzing him, while simultaneously causing him to harden.
Brook: Nami, I can't keep this up. It's too draining. (he stops)
Nami (looking at her storm cloud from before): It's the right idea, but we need something bigger. I've got it. Can you stand to do that attack again?
Brook (panting): I think so, for a short while at least.
Nami: Good, we're going to need it.
Brook: Wait, the cloud and my cold wind combined...Nami, we can't! We'd be sneering at the gods themselves to harness that power!
Nami: If they didn't want us to use it, then why do the books for it exist on the mortal plane? Besides, do you have any better ideas?
Nami: Then we're going with the sub-z stuff. Help me out here! (holding half her staff in each hand) Fimbul Tempo!
Brook (waving his arms as if beckoning the demons of the underworld themselves up from their cold resting place): Silent Requiem on the Aurora Plains!
Multi-colored light begins shooting from Brook's sword into the cloud. The cloud absorbs it as the exterior slowly freezes, solidifying, leaving the core of the cloud untouched.
Nami and Brook: FINAL DIRGE OF RAGNAROK!
Then, in perfect sync, Nami and Brook lower their weapons, pointing them at Slime. From the cloud, a beam of cold light shoots down, completely enveloping the creature. It releases a wave of some kind, causing their muscles to tense and their nerves to shake uncontrollably. They make sure to ground themselves so as to avoid equipotential shock. There is a tinkling noise like the sound of glass breaking, and then silence. When the dust clears, Slime is gone, leaving no more trace of the living disaster on the mortal plane.
Brook: Now that that's over, may I see your panties?