All roads lead to Lavos... but there are many ways to get there. Passing through the Black Dream is one. Taking the bucket Gate from the Farthest Reaches of Time is another. Flying to A.D. 1999 in the Sylbird is a third, and bypasses fighting the shell. And there's also a fourth way, but that's special...

This section assumes passing through the Black Dream to reach Lavos. For other paths, please refer to the following section.

Losing to Lavos results in a dramatic bad ending. This applies at all stages of the battle and all points in the storyline, with the exception of the battle in the Abyssal Temple that you're meant to lose.

The party finds themselves facing Lavos in a distorted dimension. "Lavos's Theme" plays, of course, though it's a special extended version now.

The image of the Dragon Tank boss from early in the game appears briefly. Lavos now has two side... somethings... that act like the tank's wheel and head, and Lavos itself emulates the tank body. After taking a pitiful amount of damage...

This time the image shows the Guard Machine from outside the food storage room in the future. Lavos keeps changing attack modes every time a mode is beaten, going through Hekeran, Junkdragar, Gran and Leon, Nizbel, the Magus (such nerve!), Azarla and the Black Tyrano, and Giga Gaia. The party gets a chance to regroup and heal between each battle.

Most of these shouldn't be a problem, but Giga Gaia could still be a threat, and don't neglect appropriate party selection and tactics especially for Nizbel (make sure to have an Aether attack handy) and the Magus.

After the last emulated boss, Lavos opens its craw (?), makes the Evil Lavos Noise, and attacks as itself. However, it really isn't all that difficult... almost too easy, especially compared to fighting it at the Abyssal Temple. Beating the head (?) reveals a gaping hole in the shell...

Unused monster data includes what appear to be unfinished Lavos versions of Melfikk, Mother Brain, Rust Tyranno, and possibly also Son of Sun. They might have been dropped due to looming deadlines, but I tend to think they were deliberate omissions. The Lavos boss rush goes on long enough already, and since all of those bosses come from optional sidequests, they would just confuse any players that didn't finish the corresponding quests.

Ayla: Beat Lavos!
Aylas strongest!!

Ayla: Lavos down!
Ayla No1!!

Marle: But it doesn't seem like
that's enough to finish it...!

Marle: But THIS couldn't have done
him in...!

Lucca: I w-wish that were
the end of that...

Lucca: I wish it were over...

Robo: From inside Lavos's body,
a still more powerful life energy
IS detected...!

Robo: I sense a powerful life force
within Lavos.

Frog: But it doesn't seem like it's
over just yet...

Frog: Will there never be an
end...?

Ayla: This Lavos's shell!
Insides still healthy!!

Ayla: This Lavos's shell!
Inside still strong!!

Magus: Don't celebrate!
It's still too soon to relax...!

Magus: It ain't over yet...

Lucca: There's no choice but to go in.
I was afraid of this...

Lucca: I guess we have no choice.
But...

Robo: We must INVADE the
interior and defeat the CORE part!

Robo: We must invade the interior
and attack its...core!

Frog: This's just armor, in the end.
Got to beat the insides to death...!

Frog: This be only armor!
'Tis what's inside that must be
destroyed!

Magus: I'll put an end to your life.
Lavos...!

Magus: We'll get to the bottom of
this, Lavos...

??? is the actual location name listed on games saved here.

The party enters the hole and drops into a cave deep inside.

Marle: We've come awfully
deep inside...

Robo: According to my sensor
readings, the core IS close!

Robo: According to my sensors,
we are close to the center!

Frog: Creepy place.
More disturbing than Magus Castle...

Frog: This is creepy.
It's worse than Magus's place...

Ayla: !!
Lavos's smell get stronger!!

Ayla: !!
Lavos smell...STRONGER!!

Nearby are both a save point and a Gate leading back to the Farthest Reaches of Time. It's not a bad idea to head through the Gate now to heal up and restock supplies. The shell stays beaten and the hole open, so there's no particular reason not to.

Old Man: The Black Dream is gone, and that
woman was at long last able to take her rest.
She was able to return to being human...
Now is the time to dive into the Gate from
the bucket over there...!
This is not just your battle.
This is between all life on this planet...
Yes, this battle is between our planet
and Lavos...!

OLD MAN: That poor woman can finally
rest, now that the Black Omen is
gone.
She's reverted back to a human...
Now it is time for you to access the
Gate contained within that bucket!
You fight not just for yourselves, but
for all living things...
This is a battle between Lavos and
the entire world!

Robo: Could THIS be...
from when WE fought?

Robo: A...hole...
Did WE do that?!

Frog: That hole...
Did we do that??

They continue inside...

As the party moves farther along the tunnel, the sounds of breathing and a heartbeat grow stronger... At the end of a tunnel is what looks like a humanoid armored creature with huge cables attached (energy? data? life support?). 3-13 世界変革の時 (When the World Reforms) plays.

I don't usually comment on the track names, but this one deserves it. To translate and paraphrase the definition from goo's dictionary function, 変革 (henkaku) means "changing and making new", so the battle will change and renew the world.

Robo: I c-can NOT believe it...!
It HAS the genes of all lifeforms
since life was born on this planet!

Robo: Amazing...
It houses all the DNA of every
creature that ever lived...!

Frog: Fight by my side...
Cyrus!

Frog: Cyrus, this be our finest
battle...

Magus: This time, I swear...
will be your last, Lavos...!

Magus: Finally...
You have met your match, Lavos!...

This stage of Lavos has a main body and two arms. The main body starts out inactive and nearly invulnerable. The arms use a variety of moves, including:

Lasers blast the entire party, inflicting magic damage. As the description suggests, this attack is only usable when both arms are present.

Negates one character's protection against status effects. This attack only seems to occur when one arm remains, so try killing both at once if possible. Note that the arm at screen right has more health than the other one.

After both arms die or enough time passes, the body becomes active (and vulnerable) and cycles through the following five abilities until dying:

Confuses any character who lacks protection, and deals some damage to all.

邪気 (jaki) doesn't translate well, but means something similar to "evil aura" or "malice". Jyaki's name is also a homophone of this.

Poisons any character who lacks protection, and deals some damage to all.

Fire damage to one character, insignificant with high magic defense.

Non-elemental magic damage to all characters.

Interesting that the name for this attack is just the names from the last three shown all at once. And yes, I did choose the words in the other names carefully so that the effect would work in English, but it was mostly a matter of picking appropriate synonyms and parts of speech. It's still not perfect—if I were to translate the final attack on its own, it would come out more like "evil shadow flames that kill your will to fight"—but it works reasonably well considering.

Roughly. Brief nonstandard kanji compunds rarely translate well.

When the body dies, the music fades. The figure the party was fighting is replaced by a smaller vaguely humanoid figure wearing what looks like a space suit.

Marle: H-human form...
D-don't tell me, it...
It couldn't be armed with the powers
of every living thing on this planet...?

Marle: It's...humanoid...
It seems like it has collected all of
the vitality from the creatures who
have lived on this planet.

The following is unused. It looks like there's a "wait, then end text block" code where there should be a "wait, then clear text and continue" code.

Lucca: I-I've figured it out.
What it's after...
It's a parasite on the planet, picking out
and collecting the superior parts of the life
forms on the planet over an extended time...
It bears children with those genes there on
Death Mountain, then on to other planets...

Lucca: Now I understand...
It lives on a planet for as long as
possible, stealing away the most vital
resources...
It combined the DNA it found here
with its own, and gave birth to those
creatures up on Death Peak.
Eventually the young must migrate to
other planets...to repeat the cycle...

Robo: TH-THIS was Lavos's goal...!
TO gain a record of the genes of
every lifeform on the planet...
and TO further its own evolution!

Robo: This was Lavos's goal...!
Using the DNA of every organism...
And achieving the ultimate in
evolution!

Frog: Wh-what the hell's going on...!?
Wait, don't tell me it's got the powers
of every living thing on this planet...
That's it! Us, and all that's developed
in every living thing on this planet...
The lowlife's been hoarding it all
while it sleeps...!!

Frog: This be evil!
Indeed! This thing possesseth the
vitality of all living creatures...
It hath harvested DNA from animals,
only to further its own evolution!
And whilst sleeping, to boot!

What are the odds that Frog would have any idea what DNA even is? Not too good.

Ayla: This like Aylas!
Like Dinomen, Pteran, Nizbel...!
Like Ayla, {char1}, all!
Smells like all...!
Has smells of all earth's life!!

Ayla: This smell like Ayla's
land!
Reptites, Ptero, Nizbel.
Ayla, and {char1}!
Smell like all people I know!!...
Smell of all living things!!

Magus: ......
It's slept underground and kept taking
the evolution of all life on this planet
as its own since bygone eras...?

Magus: ......
So...since the dawn of time, it has
slept underground, controlling
evolution on this world for his own
purpose...

No mention of controlling evolution, just taking advantage of the results.

Crono grabs his sword hilt.

Marle reaches for her crossbow.

Marle: Then that means we've
been living for its benefit!?

Marle: Are you saying IT'S the
reason we're all here?

Lucca pulls out her hammer and holds it up in front of her.

Lucca: Taking advantage of the evolution
this planet's life took so long to go through
just by sleeping, that's way too selfish...!

Lucca: Grown like farm animals,
waiting to be slaughtered...
All of our history...
our art and science...
All to meet the needs of that...
beast...

Robo assumes a battle stance.

Robo: Combat ability value is...
C-cannot measure!
My sensors feel ABOUT to break!!

Robo: Attack value is...
...off the scale!
It's shorting out my sensors!

Frog brandishes his sword.

Frog: You've GOT to be kidding...
We're NOT all living so we can
feed you, damn it!

Frog: It...is too much to bear... We
have been reared like animals...!
Our lives hath been for naught...

Ayla takes an aggressive stance.

Ayla: Not run away!
Ayla not run away!
Run away worse than lose!!

Ayla: Me no run!
Ayla no run away!
Worse than losing!!

Magus: That means we were, in a
sense, no more than Lavos's feed.
We humans, no...
all life on our planet...

Magus: We were created only to be
harvested. All people...
...and all living things...

Crono whips out his sword and his hair blows dramtically in the wind (what wind?). As others have noted, he makes as strong a statement as any of the others, without even speaking.

Marle: This is Crono's and our...
Leene's and Don's... everyone's...!

Marle: This is Crono's and ours...
Leene's and Doan's...everyone's...!

Marle enters her casting stance.

 Everyone's planet!!

 ...and I mean, EVERYONE's world!!

Lucca: No...

Lucca: Impossible...

Lucca draws her gun.

 I won't stand for such a
ridiculous evolution!

 You CAN'T expect to toy with an entire
world and get away with it!

Robo: I am a life created by humans...
HOWEVER, life IS life!
Just like Lucca, and EVERYONE else...

Robo: Human hands created me...
Which means I am a product of that
thing...I am no different than
Lucca and the others...

"A product of that thing"? How so? Anyway, he's taking a stand as part of the planet's life against Lavos, so even if that were true, it doesn't fit here.

Robo thrusts his fist out.

 I AM one of the many lives of our planet!!

 I am a part of all living things!!

Frog: For the sake of scum like you...!

Frog: My life retain'eth its
meaning...!

Frog flips into a dramatic battle stance.

 That's NOT why we're living!!

 We haveth our own will!!

Ayla: Ayla not lose!
Aylas this earth's life!

Ayla: Ayla strong!
Ayla and world good!

Ayla takes a dramatic kicking pose.

 You not this earth's life!!

 You outsider.
Not part of planet's life!!

Magus: ......
I WILL beat you this time, vermin...

Magus: ......
It's over for you...

Magus does his dramatic pose.

 I will settle my long struggle...!

 Your life ends here!

Lavos makes the Evil Lavos Noise and holds up two somethings that float to the sides. The screen whites out and fades back in to show everyone in a warped dimension different from those previously seen. 3-14 ラストバトル (Last Battle) plays as the party engages the Lavos Core.

The bit on the left absorbs all elemental attacks and uses the incredibly annoying Seal Protection ability, so kill it as soon as possible with physical attacks. The humanoid part has standard defenses, but uses the largest variety of moves, including a powerful slap and all of the following:

Changes the background, showing a distorted view of one of various eras.

Even though this doesn't do anything by itself, characters can still counterattack it. Feel free to abuse this.

A huge bolt of lightning strikes one character, inflicting non-elemental magic damage.

Physical damage to the entire party. Used only with the Primeval backdrop.

Slow status and some damage to all characters. Used only with the Ancient Era backdrop.

Hurts all characters, but at least it can't kill. Used only with the Middle Ages backdrop.

Hits all characters, inflicting minimal damage in addition to various status effects. Used only with the Modern Age backdrop.

Magic damage to the entire party. Used only with the Future backdrop.

The bit on the right is nearly invulnerable at first, but that's simple to negate. When either of the other parts dies, it's not long before the following occurs:

I've even seen characters counterattack this. It's a bit unfair, to be honest.

If it's attacked at this point, it takes normal damage, and the following message appears:

After some time passes...

Any slain parts come back to life at full health. For a time after this, attacking the right bit gives the following message:

After some more time passes...

This makes the right bit nearly invulnerable again. The right bit is the only part that really matters. It has a lot of HP, but as soon at it dies, the battle is won.

It screams the Evil Lavos Noise one last time, the background flashes through all the eras, and the screen goes white...