Chrono Trigger owned by Square-Enix. 
Images used for educational purposes only.

At long last, the final battle. Lavos is one of the strongest creatures in the game, and, wonder of wonders, it has multiple forms. Like, many multiple of forms. There are several ways to fight this beast, available as soon as you arrive at the End of Time:

- Via the bucket at the End of Time. This will take you through the standard Lavos encounter.

- Via the Epoch. If you use the Epoch to travel to 1999 once it has wings, you’ll automatically skip the first phase of the Lavos battle - though you won’t be able to save.

- During the invasion of the Ocean Palace halfway through the game. This version of Lavos is made to kill you horribly, and so is stronger than Lavos fought through any other means. Nevertheless, you can kill Lavos this way… it’s just harder. Don’t expect to take this route before you’re on a New Game +.

- Via the Black Omen. Defeat the string of three bosses at the end of the Omen and you’ll be shunted into the Lavos battle.

- Via a special Gate at the Millenial Fair. This will only appear during a New Game +.

In most cases you have to defeat Lavos in three consecutive battles, though you get a break after the first string of connected fights. 

First Phase

Initially appearing as you’ve always seen, Lavos starts off by calling upon the accumulated DNA of the creatures of the planet to determine its attacks. In essence, Lavos replicates the health and moves of many of the bosses you’ve already faced. These fights are almost universally easy, since, y’know, you’ve been there before. Here’s a quick rundown on how to defeat each one.

Dragon Tank - So weak it’s pitiful. A few physical knocks should take it out.

Guardian - Physical hits. So weak.

Heckran - Magic, magic, magic.

Zombor - Lightning or physical attacks will do nicely.

Masa & Mune - Just beat ‘em down.

Nizbel - Electricity to stun, physical attacks to kill.

Magus - Follow the elemental weaknesses, use the Masamune to lower its magic defence. Hilariously enough, Magus himself is the best counter for the first phase of this fight.

Azala and Black Tyranno - Wipe out Azala with electrical attacks, then do the same to the Tyranno before it can charge up a fire attack.

Giga Gaia - Take out the arms, then go after the body.

Once you sweep through the phases, the real fight begins.

The iconic form of Lavos takes on the party, battling over the fate of the world in 1999 AD

Lavos

Despite what the previous battles may have hinted, Lavos is no pushover. It begins every battle with a ‘rain from the heavens’ that inflicts a fair amount of damage, and will periodically use this attack again to mash your whole team. Lavos will also employ a single-hitting needle attack that can cause substantial amounts of damage to your weaker teammates, proving quite dangerous after a rain of fire. More dangerous than the rest, though, is Lavos’ capacity for confusing your whole team, which can leave your vulnerable to its damaging hits. Your best bet is to go all out, utilizing your strongest Techs and Dual Techs as quickly as you can to annihilate Lavos’ fairly low HP. It doesn’t take that long to kill the beast, and Lavos is powerful enough that you shouldn’t waste time with lower-level attacks while attempting to preserve your MP.

Once Lavos ‘dies’, there will be a hole in its shell - and that hole will remain there whenever you approach Lavos from the outside, meaning this first fight is forever done. Lavos isn’t finished yet, though, and when you enter the hole you’ll find a save point, a Gate back to the End of Time, and a northward path. This is your last chance to do other stuff in the game before the real final showdown. If you think you’re ready, though, by all means, run forward and embrace the last battle.

(If you attack Lavos with the Epoch, you’ll wind up in here without having to face the shell - but there will be no Gate and no save point. Makes sense.)

Deep within its shell, the inner Lavos fights the party a second time

Lavos

Looking slightly different this time around, Lavos is also a fair bit stronger. Consisting of a body, a left arm and a right arm, Lavos begins every battle with an all-hitting attack that is ridiculously strong against anyone without a decent magic defence. You’ll probably want to heal immediately after it hits. That done, go to town taking out the arms, as they provide Lavos with an extra layer of offensive power that needs to die. All-hitting attacks such as Luminaire and Flare are preferable, since you get rid of both arms at once that way, though focusing on a single arm to whittle it down more quickly is also possible. Getting rid of the arms will lower Lavos’s defences to killable levels, but it will also unlock a series of more deadly attacks that go after status in particular. Your approach shouldn’t change a whole lot, but you’ll have to deal with occasional bouts of poison and confusion. Aside form the occasional use of that horrifying all-hitting attack, the fight isn’t that bad.

… but it’s also not the last fight.

Moving endlessly through time, the Lavos Core engages the party in the final battle

Lavos Core

The grand finale! Lavos now appears as an oversized humanoid alien, accompanied by a pair of Lavos Pods. You’re in for the fight of your life…

… but not in the manner you’d expect. The Lavos Core is indeed your primary opponent during the final phase of the battle, but it’s not your primary target. The ‘Core’ actually has low amounts of HP for what it is, and won’t take that many hits to kill, though it’s responsible for Lavos’s most powerful attacks, notably a pair of all-hitting ‘ultimate’ moves that target defence and magic defence, doing ridiculous amounts of damage. Taking it out will buy you some time to recover, but not for long, as the true target of the fight, the right pod, will resurrect anybody you kill.

The fight runs as follows. First, take out the left pod. It has low amounts of HP, and though it neatly resists magic it will die quickly to physical Techs and normal hits. Once it is gone the central pod will start pulling out its strongest attacks. Maul it with Dual Techs as quickly as you can. Once the primary damage dealer is gone - and often even before - the right pod will lower its defence. Now’s your chance to smack it around with your best attacks for a few rounds before it brings the other two pods back to life. Assuming you don’t kill it in time, you’ll now have to repeat the process again. You can attack the right core and ignore the central one, if you want, though you’ll be exposed to some very dangerous attacks if you try.

Destroying the right pod will automatically destroy the other two pods if they’re still alive. It will also bring the game to an end. Congratulations! You’ve beaten Chrono Trigger! Enjoy the ending!

… now, can you do it again? Perhaps even with a single character? This game isn’t over yet, folks. If you beat Lavos by travelling through the Black Omen, you’ll unlock New Game +. This mode allows you to restart Chrono Trigger but keep your team’s inventory and stats. Consequently, you can attempt beating Lavos at various points throughout the game, and potentially unlock new (and very weird) endings. Have fun!

(And if you own the DS version? Oh, it’s just starting. There’s a whole other final boss you can take on… once you defeat some additional dungeons.)