Here you are. The final lighthouse. The final dungeon of the game. You'll see that the perpetual blizzards and extreme climate have taken their toll - ice blocks are everywhere.
Finding Agatio and Karst
First of all, you need to locate the terrible two that stole the Mars Star off you in the first place. Before you go inside, head up the right-hand ladder and go left up here to the base of the elevator. The chest up here contains an Apple. Go back down and enter the Lighthouse.
There are a lot of different paths you can take in this room, but unfortunately most of them are blocked for the mean time. Go up the right-hand stairs, and use Pound on the pillar to access the chest. It's a Mimic, and defeating it gets you a Cookie. Go back down. The stairs lead through a pillar-jumping room to what is, for the mean time, a dead end. You need the Mars Star to go any further here, so don't take the stairs. Go around the back of the ice blocks to the right, and go around to the door. The giant ice block can't be broken yet, so go around to the next door. Back in this room, go left and up to the door.
At the end of the path, up the stairs, Pound the pillar to crush it. If you want to save time in the coming sections of the lighthouse, set Pound to a Psynergy Shortcut, with Move as the other one. Head up to the door and around to a small block of ice. The pipes make getting the Mars Djinni impossible, and you can't get to the other door yet. Instead, use Grind on the block of ice, and you'll crack the large ice block lower down. Retreat from the lighthouse and return to the room with the now cracked ice, and use Burst to blow it apart.
Through the double-door, go left in the next room (again, make note of the ornate circle), all the way to the door at the top of the stairs. Ignore the one you go past on the way. You need to get to the stairs down on the other side of this room, but you can't get past the flamethrower statues, since the flames will cause you to leap off the platform. If you do get caught by them, leave through the door at the bottom, and go left back to the stairs. Basically, use the dragon statue in the groove to act as a barrier. Move it one square at a time - if you go too fast you'll move your cover away as a statue goes past and pushes you off.
Once you reach the end, move the statue into its hole to permanently block the flame jet, and go down the stairs. Descend the stairs to the left and on the patch of ice, go left, up, right, down, left to reach the other side. Through the door, use Blaze to send flames onto the torch, which in turn activates the dragon head. It spits a massive fireball at the block of ice, causing it to crack. Go back across the ice in the previous room and head through the door beneath the staircase you came down. You can use Burst on the ice here, but the door only leads to a Reveal symbol which hides an ornate circle. Which, again, you can't use.
So, go right through the door. Climb up the ladder and use Blaze to light the torch and cause the dragon head to blow apart all the ice blocking your way. Go down through the door, and take the first door you come across. Get the Orihalcon from the chest, then go back to the corridor and head along to the next door. Head up both sides of the ice channel in this room and use Pound on all the pillars. This will open up a series of safe spots you will need to get up to the door without being blown back by the dragon head's fireballs. Once you're through the door, head left to the next door.
Before you get on the ice patch, Move the left dragon statue to the left. It will slide across the ice to another nook in the ice, but this will allow you to navigate the patch to reach the door. Go down, left, down, left, up, right, up, left (you'll be next to the statue you pushed), down, left, down. Confront the Mercury Djinni here, and Balm will join your party once you beat it. Set it to Piers or Mia. Then, go straight up and you'll slide to normal ground. Ascend the stairs and go up the staircase. Slide down the groove and you'll reach the Teleport Lapis! Equip this on Sheba. Now, you can instantly go to any town you've visited on the map, as well as use the ornate circles around the lighthouse to get to previously inaccessible places (these ornate circles have appeared in other places, like Contigo, and Teleport is necessary to get to most of the extra summons you'll be going for soon.
Once you've got it, use Teleport when standing on the ornate circle beneath you to teleport directly downwards to the next circle. Now, go left, and back through the flame-spitting statue room. The extra tiles jutting out serve as a means of getting around the flame jets without using the pillar, but you needed the pillar the first time because the last flame jet can't be dodged. Back down the stairs, head through the door below, then left to the double doors (use Burst down the stairs on the crack in the ice if you haven't already). Use Reveal, then Teleport on the hidden circle and you'll be on the platform in the room where you got the Orihalcon previously. Go down the stairs.
For this next room, before you use the groove, go down and left below the blocks. You will see some of the challenges you'll be confronted with when you run this gauntlet in a few second's time, but at the end you can climb the ladder by the torch (you can't light it) and grab the Valkyrie Mail from the chest, this boosts unleash rate, give it to Isaac or Felix. Now, head back to the groove, but don't slide down it.
You've got two choices. You can either give yourself a challenge and attempt to run the gauntlet, in which case you should make sure you have Pound assigned to a Psynergy Shortcut, or you can cheat. If you decide to challenge yourself, it isn't that hard - just use Pound on every pillar, go across the top of the ice patch, and take the top path at the end of the ice patch to avoid the dead-end. Cheating simply requires that you slide down and hit the button, and don't move. You have to get to the end before the flame jet reaches the torch and sets off the dragon head, which blows you all the way back and down a hole to the floor below (you have to climb up and try again). But, if you stay on the button, you're not in the firing line, and when the dragon head fires, it clears away all the ice and all the Pound pillars, leaving a simple and untimed walk across to the door. Either way works.
Once you're through the door, ignore the Teleport circle for the mean time. Head along the long path via the door at the top. The Teleport circle leads to the one in this room, but as you can see, the moment you get there you'd be blown off the side by the dragon head's fireballs and have to go all the way back. But, since you're here, climb the ladder and move the dragon statue across into the slot. This blocks off the flame jet, and the dragon head can no longer fire. Go back to the Teleport circle, and Teleport to this familiar room. Go up the ladder and through the door at the bottom.
At the end of the long path you will reach a room with various pillars and ice patches. The stairs down lead to an empty floor which is where you go down to if you slide off any of the platforms by accident. Getting the chest in here is imperative - it contains the most powerful weapon in the game, the Sol Blade. To get it, follow this path using the left-most path of pillars:
Down, down, right, up, right, down, right, down, down, down, right, right, up, right, up, up, up, up. Grab the Sol Blade, then you can use the ice to go down a floor and return to the pillars. To get to the exit, go:
Down, down, down, down, right, down, down, right, down. Follow the long path down various staircases to reach a room with a channel of ice on either side. Keep going up until you reach two dragon heads by an ice block, with two real dragons frozen within. Don't bother putting any Djinn on standby, since the extra health will help you out a lot more than an initial summon rush (you don't want to have to resurrect anybody, right?). Save, then use Blaze on the torch to light the other one. This will crack the ice block. Use Burst to crack the ice, and the dragons will attack.
Boss Battle: Flame Dragons
You'll notice that one of the dragons is bigger than the other - incidentally, it has more HP and a moveset similar to Agatio's. The smaller dragon has less HP and has a moveset similar to Karst's. Anyway, for this battle, just slowly work through unleashing your Djinn until you can summon. Eclipse and Haures should do good damage, so just repeatedly summon them when you can. Jenna's Cool Aura as well as Mist Potions and Felix's Flower can help to heal everyone when they need it, and you don't need to worry about resurrecting since you have a backup party as well.
A constant stream of attack Djinn followed by Eclipse and Haures will finish off the bigger one. After that, heal up (don't forget good old Shade, or Granite and Flash from the original Golden Sun Djinni to help reduce damage) and use the same method to dispatch the other Flame Dragon. You get a Psy Crystal for winning.
When outside of the battle, you'll discover that the Flame Dragons were actually Agatio and Karst transformed. Anyway, grab the star when Agatio drops it, and take it up to the dragon head. Use the Mars Star, and the lighthouse will warm up again. Lava will flow in the channels of ice. Pick up the Mars Star when it drops out, and Retreat from the lighthouse. Go back inside to the first room.
The Elemental Torches
You can now use Blaze on the lit torch up the left-hand stairs to activate the dragon head. This clears the ice blocks away in this room and cracks the large block of ice. Use Burst on the crack to blow the ice apart, then go through the uncovered door. Use the stairs at the top of the next room and follow the corridor along to Fugue, the Mars Djinni. Save before you confront it, and defeat it in battle. It'll join your party, so set it to either Garet or Jenna. Back in the first room, use the stairs in the centre to go up to a series of pillars on the lava. The path is:
Left, down, left, down, right, down, down, right, right, up, right, up, up, right, up. Use the stairs to reach the next floor. Up the stairs, the dragon head will speak.
"You who hold the star, open your heart and listen...If you wish to scale the heavens, set the four spirits aflame!"
Then, a few doors will flicker in the walls with the various animals on it, then disappear. Before, these doors weren't there, but now you can approach the walls to make the doors appear. Now, you have to complete the path of puzzles behind each of the doors to ascend to the top of each of Mars Lighthouse's side towers. You can do them in whatever order you like, but this walkthrough will start off with the bird symbol - wind.
The Bird Symbol
Go through the door in the bird symbol and follow the path to reach the outside. Go up the stairs and follow the bridge to the side tower. Inside, take the left-most Cyclone portal. At the top, take the left-hand portal and move the statue down below in front of the flame jet. Drop down the groove then use the chain of Cyclone portals up the ladder to the right in this room to get back to the first room in the side tower. Take the left-hand portal again, but this time at the top use the right-hand one. If you went this way before you'd be shoved off by the flame jet and forced to go back again, but now that it's blocked off you can go up to the ladder.
The flame jet can't be dodged yet, so go down the ladder and use Reveal where the symbol is to reveal a Cyclone portal you can take. Go around to the next portal down, and use it. Wait for the flame jet to go up and to the left, then quickly run to the left and use Move on the piece of Hover circuit to move it into the hole and complete the circuit. Now, let the flame jet push you off. Climb up the ladder to the left, and you can use the now active Hover pad to float over the flame jet and reach the central Cyclone portal.
There's a nasty surprise waiting for you at the top of this portal - a large dragon head spitting fireballs. The moment you arrive, run to the left and grab a Psy Crystal from the chest. There's nothing to the right, so the only way is down. Wait until the dragon head has just spat a fireball, then run down the channel. At the bottom, use Reveal (notice the symbol) and hop across to the right. You have to do this quickly, before the dragon head spits another fireball and sends you down a level. Go down to the door and you will emerge outside at the top of the Wind tower.
Go up either staircase and you'll notice the Bird symbol again, along with a purple flame. Use Blaze on the purple flame torch to launch a jet of purple fire at the bird symbol, making it glow. One of the torches back in the original room will light up purple. Now, Retreat, and re-enter. Hop back across the pillars to the torch room again.
The Fish Symbol
Now, you'll want to go through the door in the fish symbol. When you're outside, follow the long bridge to the next side-tower, and go inside. Go around to the stairs at the top. On the ice patch, go left, down, right, up, left, up to reach some stairs down. This is a pipe-moving puzzle similar to one's you may have encountered in Mercury Lighthouse if you played the original Golden Sun. Anyway, hug the left-hand wall until you reach the pipe section already in place. Push this up, then go to the right and freeze the top puddle. Freeze the other one as well. Go back around to the top of the room, then push the vertical pipe section right, and the top horizontal pipe section down. Both the ice pillars you made will stop these in place. Go back around to the last remaining pipe section and push it up to complete the pipe. Now, go back up the stairs into the previous room.
Slide off the side of the ice section and use the stairs to get back up. Now you need to navigate the ice patch by going left, down, right, up, right, up, and use Blaze on the torch at the top of the ladder when the gas jet is in reach of the flames, and it will ignite, and in turn it will activate the dragon head. This will blow away some ice. Slide off the ice by going down again, then from the same entry point as before, go left, down, right, down, left on the ice patch to reach the next door.
Follow the path outside and at the top of the stairs, use Blaze on the blue flame to make the fish symbol glow. Now, Retreat back to the beginning of the lighthouse, and follow the path back up to the torch room.
The Human Symbol
Climb the right-hand stairs and go through the door in the human symbol. Follow the path around to the next side-tower. Inside, Move the right-hand statue to either side to uncover a door (behind the others are flame jets that will blow you back). Hop across the lava and go through. In the next room, ignore the door in front of you and Move the left-most statue to either side to uncover another door. Hop across and go up the stairs.
You now need to solve a simple Carry puzzle - Carry the two blocks on the platform into their respective holes on the ledge above, then move the block up the ladder across using the blocks as bridges until you can use it to get past the flame jet. Walk past the flame jet and use the tightrope. On the other side, push the statue off to open up a shortcut. Now, you need to get past the flame jets to the left. There's no extra ground to dodge them, but there are small squares of sand. Wait until you can run to these, then use Sand. You should be able to hide under the flame jets until they go past, then turn back to normal and continue left. Once you're past, climb down the ladder and head out the door to the bottom.
Go up either of the stairs to reach the yellow flame torch. Use Blaze to make the human symbol glow, and then Retreat from the lighthouse. Re-enter and return to the torch room.
The Dragon Symbol
Back up here, go through the final door - the one in the dragon symbol. Follow the path until you get outside. When you reach the side-tower, don't go in - instead, go around the other side. Here, there's a chest containing Alastor's Hood, which you should equip on whoever has the least Defence. Now, go inside the side tower.
In here, use Burst on the crack in the wall to the left. Follow the path of hopping stones across the lava to reach a button. Press this, and the flame jet will ignite and move across to the torch, setting it alight. Return to the first section and use Burst on the other crack in the wall. Follow this path of hopping stones to the stairs. Go up them and use Blaze on the torch to shoot a jet of flames across to the next torch, activating the dragon head and cracking the middle section of wall. Now, return, use Burst on this middle section, and hop across the stones to a ladder.
Go around the top of the dragon head, descend the next ladder, and hop across to the stairs. In this large room, push the horizontal section of pipe below you up into place, then go right in-between the pipes. When the path forks, go down and around to where the flame jet is. Use the stairs to go under the pipes, and on the other side, Move the statue one space to the left. Go back to the fork and go right. Go underneath the pipes using this set of stairs, and when you reach the dead-end use Move on the statue to move it across to the left one more space and block off the flame jet. Go back around to the fork, and go down. Instead of going down these stairs go across the top of the grate and past where the statue blocks the flame jet.
Use the next set of stairs to reach the horizontal pipe section you pushed earlier. Shove it out of place, then return to the last flame jet you passed. It's now inactive, so you can go past it. Follow the path to reach the door to the outside. Climb the stairs and at the top use Blaze on the torch to light up the dragon symbol. Now, return to the beginning of the lighthouse YET AGAIN using Retreat, and go back to the torch room.
The Side-Quests
When you first arrive at the top of the stairs into the torch room, the large four-eyed dragon head will speak again:
"You have proven your worth! The heavens await you!"
And with that, the dragon head will blow a fireball that uncovers a Teleport circle. This leads up to the aerie of Mars Lighthouse, and you expect there to be a big battle at the top, right? There is indeed one, but with your party as it is, you're not in the best position to go about fighting it. After all, it is the final boss battle of the game.
What you should do now are the four main side quests. These are Yampi Desert Cave, Sea of Time Islet Cave, Treasure Isle, and Anemos Inner Sanctum. Each of these lead to the really powerful combo summons, as well as the last remaining Djinn you need and lots of items. So, save, then leave Mars Lighthouse. Don't bother returning to your boat - you can Teleport instantly to wherever you like, and your boat magically teleports with you.
A separate section of this guide, accessible from the main Golden Sun: The Lost Age page, goes through how to get to each of the side-quest dungeons, how to complete them, what boss you face, and what you get there. If you don't want to do the side-quests, then use the Teleport circle that the dragon head reveals and proceed across the floating platforms until you reach the Lighthouse's well. A scene will appear, and you will confront the Doom Dragon. This boss fight is described on the next page.