
Okay. Let's try again.

This time I manage to land the Elixir for full damage, and Lugaeborg decides to Reverse Gas immediately after. This means Yang and Kain aren't deadweight, throwing Hi-Potions at worst, and can actually punch and stab Lugaeborg a bit.

That works, finally.

Then Yang stuffs himself into a cannon to keep it from firing and is removed from the party. Goodbye, Focus Punch. You were super-effective.
Then Cid joins the party. Then Cid blows himself up. Okay, bye I guess.
I do appreciate that Cid's last words before he goes over the gunwhale of the airship with his bomb is a response to Rydia's "But you'll die!" with "And so young, too!"
So I go find Namingway in Agart and he's like "Hey, I really like this girl, I'm gonna give her a Rainbow Jelly. Do, uh, do you have any Rainbow Jelly?"
and you're like fine whatever
Stop in with the fat chocobo and check the bestiary, you'll find that Rainbow Pudding is the rare drop from all of the slimes you've seen so far. Red Mousse live in the Watery Pass, Yellow Jellies live in the Antlion Cave, and Purple Bavarois live in the Tower of Zot. We can't go back to Zot, so that leaves the Watery Pass or Antlion Den.
The Antlion Den second floor is almost entirely populated with Yellow Jellies and Land Turtles, so... let's go there. Thankfully, both of those are such earlygame dungeons that even Rydia can smack a Yellow Jelly to death with her rod. So that's cool.
At this point I was going to post screenshots of how many Yellow Jellies it took to get the Rainbow Pudding. Potion, nothing, Hi-Potion, nothing, Potion, Potion...
Then I got to 40 and decided that was too many. I'd have to put it in text. Potion, Potion, Hi-Potion, nothing, nothing, Potion, nothing, nothing...
Everyone gained a level. Rosa gained two. After 100 fights with Yellow Jellies -- not counting Land Turtles, Leshys, Goblins, Sand Worms, or whatever else -- I got sick of it and just used a cheat code to force the drop.
I then took it to Puddingway and forked it over. Man, when do you get the augment that makes rare drops easier to find?
I guess I got a little overzealous in deleting those 100 screenshots of post-Jelly rewards, because I don't have any documentation that those were the events that transpired. Oh well. You're seriously not missing anything.

Airship crew, hook, hovercraft, Eblan. The passage through Eblan has a grave near one of the secret passages, but there's no way to investigate it. It doesn't seem to do anything.
The chest has a Blood Sword inside, so I guess there are supposed to be
implications.

Rubicante uses Inferno, not Glare, to do his ridiculously high damage. Like Meltdown in Final Fantasy 6, it hits everyone on the field, not just the enemy party -- but Rubicante, of course, absorbs fire.

It doesn't matter how fragile Edge and Kain are if Cecil is the only one getting hit, right? Maybe I can put Cecil in the back to cut damage in half again, and make things even easier...?
(Not really. Cecil's damage output with Counter is as much a part of the strategy as cutting incoming damage. And he does half damage from the back row.)
What's New: Getting into Babil is less "ninja trickery" and more "actual teleport"

The lower floors of Babil are a maze. The floors aboveground are just long straight "hey, how many steps can we make you take?" paths.

King and Queen Eblan take their sweet time reverting to sanity and talking to Edge, but there's nothing new there. So, Rubicante.

Rubicante is a simple archfiend of simple strategy. He flings his cape open, uses Inferno, closes his cape, hits with his fist, then starts over.
Here is what it looks like after one (1) application of Inferno.
Beyond that, and try not to be too shocked here, but his counterattacks are what make him a difficult boss. Nearly anything you hit him with, he counters with Fira against the whole party. It's not as devestating as Lightning from Barbariccia, but Barbariccia didn't have Inferno.
What's the Same: Rubicante is weak to ice with his cloak open, and absorbs ice with his cloak closed. They did fix the bug where he absorbs fire with his cloak open and is weak to fire with his cloak closed, though. Now he always absorbs fire.
After struggling with Lugaeborg interrupting my actions with Reverse Gas between the queueing of a spell and its casting, I decide to skip the whole thing and just hit him with Quake rather than trying to decide whether I have time to cast Blizzara or not. He always takes normal damage from elements that aren't fire and ice.

What's the Same: If you hit Rubicante with a fire-elemental attack, he will counter by casting Raise on everyone in the party. So after he uses Inferno, throwing a Bomb Fragment at him is a good idea.
What I'm Pretty Sure Is New: If you cast a Summon on Rubicante, he counters with Blizzara.

On
himself.
Presumably it's to teach the player "Hey, moron, when he said the cold of Cocytus couldn't breach his cloak, it means
don't cast ice spells at him when his cloak is closed, he absorbs it."

But he still does it when his cloak is open.

Ninjutsu Flame, Flood, and Blitz are just Fira, Blizzara, and Thundara renamed and targeting the whole enemy party by default.
What's New: -ra level Earth spell too.