Most of the puzzles are fairly easy to work out, but there is one that can be quite annoying if you have AI companions. In the area with the large locked door, there are five switches that need to have boxes on them, and only three boxes available. The nearby switch raises two platforms, each of which contains a box, but you need to act fast to push the box off the platform before time runs out. The annoying thing is that AI companions will constantly get into the way as you try to move it. Eventually, you'll get it, though, which will allow you to grab the key and eventually reach the area's boss.
During the Buffasaur battle, the AI companions more than make up for their earlier ineptitude by constantly pelting the beast with magic, particularly Blizzard-based spells that can freeze him. That allowed me to simply unload on him like normal, dodging his attacks when necessary. He was down in a flash. Grab the Buffasaur horn and you'll automatically exit the Aqueducts. Get back to the library, give Larkiecus the horn, and he'll make the medicine. Take it, return to the village, and Eryll will be healed.
The next morning, it's off to the library to repay the favor and help Larkiecus with his errands. Speak with him and he'll explain that the city is located between two mountains, each of which has an ancient ruin on its peak. However, the ruins have been damaged, and he wants you to visit both locations to repair them. Before departing on your journey, make sure you upgrade your gear.
First up is Ice Mountain. In the first area, proceed north and jump on the handle to open the gate. In the second room, freeze the pot and toss it into the water. Continue on, using freeze pots as necessary to solve the various puzzles. There's one puzzle here that requires you to freeze and melt the ice several times, and it can be tricky. Just make sure you note where the underground switch is before you freeze the water, then move the block over top of it before you melt it. The rest should be easily reasoned out. Once you get to the save point, get on the zip line, and jump off at the right time to land on the ledge below. Exit south, defeat all the enemies, and a block will appear up near the ruined archway. Push it into the center and a pillar will rise up out of the ground.
Report back to Larkiecus, and you'll learn Fire Mountain is your next destination. Once you get there, head to the right in the first room and use the exploding barrel to open the passage to the next area. Here, use the water barrel to douse the fire, then quickly and carefully jump across to the other side. The platforms fall, and if you wind up in lava, you'll take major damage. Jump and grab the level to make the exploding barrel appear, and use it to move on to the third area.
Continue on in like fashion until you get to an area where the enemies are carrying exploding barrels. Here, you need to defeat the enemies and use the barrels to blow up four blocks, each of which covers a switch. Step on them all, grab the key and continue north. In the next location, simply grab the water barrel and high-tail it upwards, dodging enemies along the way. Put the fire out, save, and proceed for the boss fight against the Lava Spider. Honestly, this fight was a piece of cake, as my AI companions pelted the monster with Blizzard spells and I alternated between hitting it with the nearby water barrels and hacking away. After the battle, collect the loot, then grab a barrel and jump onto the giant switch to reach the summit. Push the block into place and once again you'll be back on the world map.
With both pillars now up, return to the town library and talk to Larkiecus. With your debt paid in full, its time to head back to the village. However, the story sequences that follows your exit from the library clearly foreshadows that the old man was up to something sinister. Sure enough, when you return home, another scene plays, and when the main character awakens the next morning, he finds that the crystal has shattered, nearly all of the villagers are gone, a new tower has sprung up on the horizon and that monsters have been spotted in the library. What in the world is going on? The only way to find that out is to delve deeper into Final Fantasy Crystal Chronicles: Echoes of Time.