The name I render "Tarta" is an obvious reference to tartar (sauce), but isn't spelled the way it ought to be in Japanese (タルタル). As for the chapter name, tartar sauce is often served with fried seafood, and while I don't eat frog (frog legs?), I suppose it could be considered a sort of seafood. As an extra side note, tartar sauce uses mayonnaise as a base and may have vinegar added for flavor, and apparently it's sometimes mixed with soy sauce in Japan, too. Refer to the names of the Magus's minions if these references don't mean anything to you.

With the kid gone and battles over for now, the music reverts to "Underground Waterway". There are only a few things of particular interest on the mountain, and it's possible to sneak by many of the monsters. Jumping off a waterfall in one place nets two useful accessories, the Silver Earrings and Silver Pierce. Just before the save point is a furry creature that initially appears unimportant...

...but says something different if spoken to again...

...which is suspicious, but trying again just goes back to the first line...

...which might seem like the end of it, but with one more try...

: You guys sure are stubborn.
I'll give you this.

...and being a nuisance is worth a Magic Capsule in this circumstance. A Speed Capsule glimmers on the ground not far past the save point, and the screen after that hides a Gold Suit behind a tree branch right by the entrance. Careful timing can avoid combat with the rock-throwing Freelancer and dozing Ohgans, but it's tricky to pull off. Just past it, Crono and the others reach a cave at the top, where "Manoria Abbey" plays and a nondescript boy runs around.

Child: I'm the wind.
whooshwhoooosh!

KID: I'm the wind!
Whoosh!

...and there's the sword in the back of the cave. It sticks out of the ground, on a raised platform, in a beam of sunlight, and looks pretty impressive. However, when Crono approaches it...

The boy runs up and stands in front of the sword.

Child: Did you guys come to take it too?
The Grandleon.

KID: Are you here for the Masamune?

Well... yes, actually.

Child: Huhn, I see.
Hold on a sec...
Hey, Gran, big brooother!

KID: Thought so...
Wait a second, okay?
Oh big broooother...
Where are you, Masa?!

Another nondescript child steps from behind the sword.

Gran: What's wrong, Leon?
Aw geez, not again...
You wanna get the Grandleon and
win yourself fame as a hero, right?
Ridiculous...

MASA: What is it, Mune?
Not again!?
So! You want to get a name for
yourself by grabbing the Masamune?
What a buffoon!

Gran spins around once each time he talks, and Leon does two little hops every time he talks.

Leon: Humans are so dumb.
Even though it's how you use the power
you've gained that's important...

MUNE: Humans are so...silly!
It's how you USE the sword that's
important...not who owns it!

Gran: Not even getting something that
obvious is what makes them human.

MASA: You can't even understand
something as simple as that.
That's why you're human.

Gran: What else? We test them.
We're gonna play with them for a bit.

MASA: The usual...test them.
You can entertain us for awhile.

Leon: Yeah! Here we gooo!!
whooshwhoooosh!

MUNE: All right!
Here we go!!
Whooosh!

The two of them jump off the platform, transforming into creatures that look kind of like golden human-sized variants of the common goblins.

Boss battle! Attacking Gran (Masa), the one with the green collar, provokes a counterattack similar to Crono and Frog's X-Slash. Focus attacks on Leon (Mune), the one with the purple collar, to avoid counterattacks. The two are basically the same otherwise. Naturally, the default target is Gran.

Damage either one enough and...

...the battle ends.

Gran: We haven't had this much trouble
dealing with anyone since Cyrus.

Gran: What else?
It's time to get serious!

MASA: Yeah.
We mean business!

Gran moves to one side and poses as he says...

Leon moves to the others side and poses similarly as he says...

The two dash toward each other, meeting in the middle and yelling...

It looks like "confusion", but since that doesn't make sense, and they're definitely fusing, I think the コン is 魂 (kon, soul).

They sort of melt together, and reform as a giant yellow over-muscled brute, with horns and an oversized mouth. This is no ordinary boss battle. 2-17 ボス・バトル2 (Boss Battle 2) plays instead of the usual boss music.

The beast hits hard, has lots of HP, and has a whirwind attack that can confuse a character. Additionally, every so often it stops and opens its mouth wide...

While storing energy, it doesn't attack, but will counter all attacks with something similar to Crono's Wind Scythe, and futhermore unleashes a devestating tornado attack when done charging. But there is a way to stop it. As mentioned by one of the townsfolk earlier, try using Wind Scythe...

...which makes the brute go back to using normal attacks. Gran and Leon (Masa & Mune) take only 4/7 normal damage (about 57%) from Aether-based skills, but all other damage types work normally.

Eventually, Crono and the others are victorious. The brute splits back into Gran and Leon, who go then revert to looking like little kids. "Manoria Abbey" resumes.

Leon: Could these people
be the ones to fix us?
Will they find us an owner
like they should?

MUNE: Will they fix us?
Will they find us an owner?

Gran and Leon walk up to and into the sword. It glows and vanishes, revealing a damaged hiltless blade.

Robo: This sword IS the
legendary Grandleon...
However...
considerable time HAS
passed since it broke.

Robo: So!
The Masamune is not just a myth...
But it has long been broken.

Lucca: This is the Grandleon...
But, this legendary sword...
looks like it broke quite
some time ago...

Lucca: So this is the Masamune...
But it looks like it's been broken for ages.

The internal storyline progression tracking variable is now 0x60.

Gran: I'll give you a ride on the wind and
carry you right to the mountain base.

MASA: Allow me! We'll ride the wind to
the base of the mountain!

The winds picks up and carries Crono and the others to the base of the mountain.

Remember that house from before? The scared boy from the mountain entrance is there now.

Tarta: I-I'm sorry...
The truth is that a seriously
drunk frog man dropped this
Hero Badge in the bar.
Then when I went to the city hoping
to sell it for a lot, everyone made
a big fuss about calling me the Hero,
so I was in too deep to back out...
But I just don't have what it takes.
Legendary hero, as if...
I've learned my lesson now.
I'll give you guys this badge!

TATA: I...I'm sorry everyone.
Some frog guy dropped this in a
cafe.
I thought I'd sell it, but then
everyone started calling me a
"Hero."
I couldn't bear to get rid of it!
I just can't fake it any longer.
I'm no Hero...! I'm so ashamed!
Here.
Please take this!

Tarta's father, standing nearby, hears all this and freaks out.

Tarta's Father: Jeez, I thought it
might be something like this...
Your father's ashamed to the
point of tears!

TATA'S FATHER: Scoundrel!
I knew this was all a sham!

The internal storyline progression tracking variable is now 0x66.

Clearing the game at this point leads to the alternate ending "The Unknown Past".

Tarta: This even though YOU'RE the
one who was all boasting about,
"I'm the dad who raised the hero"...!

Well, we only know of one frog man... time to return that badge.

Frog is still standing silently in the corner.

Frog: You've come again...?
Mh, that badge...

Frog: Thee hath returned?
Th, the Hero Medal!

Have I mentioned that the fake early English in the NA version sometimes makes me cringe in agony? Seeing "Thee hath returned" is one of those times. It should be "Thou hast returned" is he's talking just to Crono, or "You have returned" if to all of them. "Thee hath"...? That's using an object as a subject and a third-person verb with a second-person pronoun. Geh.

Frog: But I'm impressed you found...
Mh, that badge...!?

Frog: You hath done well to find
this locale.
Th, the Hero Badge!

Frog: I see...
So you met that runt...
But I can't do a thing against
the Magus anymore...

Frog: Aye...
Then thou hast seen the lad.
Yet there's nary a thing I canst do
against Magus.

Frog: You need the legendary sword
Grandleon to fight him, and it's...
Besides, I have no right to hold
the Grandleon anyway.

Frog: The legendary Masamune is
required to fight Magus.
And I've no right to wield it.

Frog: Won't you just leave me alone
already...?

Frog: Please leave now...

Frog finally moves, revealing something shiny... The party checks, finding a sword hilt. "Manoria Abbey" plays.

Lucca: A broken sword...
It's a piece of the Grandleon!

Lucca: A broken sword...
It's part of the Masamune!

Robo: A sword that has been broken...
It IS a piece of the Grandleon!

Robo: A broken sword...
A part of the Masamune!

Robo: Something IS WRITTEN in
an ancient era's hieroglyphs.
I SHALL try decoding it...
............
...h... c... s... o... b...?
Hcsob...??
OH, it IS inverted!
"Bosch" is inscribed.

Robo: Something is written in
archaic script.
I will translate...
.......
R...o...i...h...c...l...e...m?
Roihclem?
System error!
I reversed it!
It says "Melchior!"

ュシッボ is particularly odd-looking, since the small ュ is only used after other characters.

Lucca: Something's engraved in symbols
from an ancient era. I think it's
simple enough that I can manage.
U... mm...
...b... o... s... c... h...?

Lucca: It's engraved with archaic
letters.
I think I can read it.
Um...mm...
...M...e...l...c...h...i...o...r!

Marle: "Bosch"? That Bosch?
The one in Medina Village...?
W-what's going on, Crono?

Marle: Melchior?
That guy in Medina Village?
What does this mean, Crono?

Lucca: "Bosch"!? It can't be...
the one in Medina Village...?

Lucca: "Melchior?!"
That guy in Medina village?

The internal storyline progression tracking variable is now 0x69.

The usual music resumes.

Frog: There's no one left in this
world anymore who can fix
the Grandleon...

Frog: Nary a soul remains to
mend'eth the Masamune.

It's "remaineth to mend", and there's no apostrophe in "mendeth" anyway...

That's not going to stop Crono from trying... Let's see if Bosch knows anything.

Bosch is here, selling weapons, as always.

Upon speaking to Bosch, the internal storyline progression tracking variable becomes 0x6C, starting the next chapter.

Retrieving the Grandleon could make a difference, but it hasn't so far. The party also recovered the badge and the rest of the Grandleon, but didn't do anything with any particular historical impact.

Also, recall that the king was injured fighting and only withdrew from battle because Tarta appeared and was mistaken for the hero. The royal family has no children in evidence yet, so with Marle as their descendant, we can be fairly certain that the king survived in the original timeline as well. Since we now know that Tarta obtained the badge recently when Frog dropped it, and it doesn't look as though Frog had any interest in revealing it to anyone himself, this may suggest that he would have left the castle and subsequently lost the badge even in the unaltered timeline. On the other hand, if he had stuck around, it's possible his contribution would have kept the situation from growing dire enough for the king to risk going into combat personally. Going by the attitude of the other soldiers to Frog and his evident inferiority complex, though, I'm leaning towards the phony hero being part of history all along.