Before entering this floor, Monica noticed that Max's wrench is, according to her, not powerful enough for the local monsters. Thus she granted Max a number of crystals and synthesis points for his current weapon.
Upon entering the fourth floor, Max and Monica noticed the missing Firbits that were looking for Holly. However, they did not want to leave due to having drunk the water from the Swamp located a short distance away. Three of the Firbits were idling, but a fourth was spending his time fishing. Upon approaching him, he appears to be thirsty and asked Max and Monica something to drink, notably Grape Juice, their most favorite drink. They gave him the juice and in return received a Fishing Rod and some Mimis.
They then walked past a much larger lake, the real fish monster swamp, and run into Master Utan, who was very weak for having eaten food belonging to the 'Holy One', namely Poison Apples. The 'Holy One' is a massive fish monster, known as King Mardan, who was also responsible for the Firbits' behavior. Using poisonous apples as bait, Max and Monica managed to fish up King Mardan and he agreed to restore the Firbits' behavior after receiving a Priscleenfish so he could clean his body.
The Firbits returned to Sindain and aided Max and Monica with the Carpenterion, introducing them to Georama. Later on, Master Utan recovered from his sickness and lifted the boulder blocking the exit path, leading deeper into the woods.
Max and Monica eventually reach the end of the path and enter Rainbow Falls, home to a wide waterfall landscape and a small pond. They proceed to plant a Lafrescia Seed received from Jurak, and later use a Sundrop obtained from a Himarra to bloom a giant Lafrescia Flower. Upon climbing to the top of the flower, the flower managed to attract the Rainbow Butterfly, which began attacking Max and Monica. After defeating the Rainbow Butterfly and restoring its sanity, it revealed itself to be Holly in human form. Holly explained her disappearance to Max and Monica, and gave a letter to give to the Firbits, and left afterwards.
The time trials here are easier to obtain, considering you now have at least four minutes rather than two in the Underground Water Channel. You have more time now to search for a key or for the Mimics, as long as you know where to go. But you still do not have time to collect the ABS and Gilda and to open all the chests at the same time. It is very useful to have Pau in your party, as he can spot Mimics and gives you the map layout of the floor at the very start.
Erik's Improved Bombs are the quickest way to take out almost any enemy in the item only stages. However, if you want to save Improved Bombs, it might be useful to throw Poison Apples at monsters and follow up with Bomb Nuts or Stones. The Molers and Pixies are particularly annoying to take out, so remember than you can pick up other monsters and throw them at each other, stunning both and taking them out with bombs.
Spheda medals in this area are granted fewer hits than other dungeons; however, this is balanced by the fact that there are spaced trees where there would otherwise be walls in other dungeons. This is a mixed blessing, though, considering the tree-filled spaces are off course and will cost you your shot in the case it doesn't get all the way through the trees. This makes the Spheda medals more random than anything else, and can be very frustrating to play.
Upon entering the floor, talk to the rightmost Firbit fishing near the small pond. Giving him Grape Juice will exchange for his Fishing Rod and some bait, which will be needed later. Talking to Master Utan at the end of the floor will initiate a cutscene that will prompt Max and Monica to search for King Mardan. Just go to the giant swamp and use a Poison Apple as bait, and fish him out. King Mardan will then ask for a Priscleen fish, which can be fished out of the small pond.
After giving King Mardan the fish, he will free the Firbits from his spell, and you may return to Sindain to get started on the georama. Conda will give you some free items, and he will be in the back of the Blackstone One to sell you materials. Returning to the fish monster swamp, Master Utan will lift the boulder blocking the path, allowing access to the next floor.
Rainbow Falls is at the end of the dungeon, but the Rainbow Butterfly will not appear without first completing Sindain's georama. First, a Lafrescia Seed obtained from Jurak needs to be planted, then its growth must be sped up using a Sundrop obtained from a Himarra by using Monica's monster transformation. After the Lafrescia Flower blooms, it will attract the Rainbow Butterfly, just climb the flower and you may proceed to fight it.