After the group is returned to the Airship Celsius, Buddy then reports that there has been a major outbreak of fiends. The girls decide to help contain the situation and put hunting spheres to the side for the moment. Besaid Island and Kilika become Hotspots. As does the headquarters of who you gave the stolen sphere to. Djose will become a Hotspot after you visit Besaid and Kilika, so best to visit there if you want full completion. But before you travel anywhere, make sure you watch any spheres you have collected if you haven't already.
If O'aka's debt has been paid, it is also at this point that he will jump ship and set up shop at the Lake Macalania Travel Agency. This shop is the best one in the game. If it hasn't been paid, make sure you do so before the end of this chapter so you can have access to this shop.
The fiends in this chapter have become more difficult to defeat. Many now have the ability to instantly inflict KO or status ailments. When you defeated Leblanc, you received a Charm Bangle. (You may have gotten a second one if you used Steal or Sticky Fingers on Baralai during the battle with him. You don't need two, though, so just sell one of them). If equipped to one party member, it will eliminate any random encounters with fiends. This can come in handy if you are trying to quickly finish missions. But it's best not to have it equipped all the time because you will want to use this chapter to level up your party by battling fiends. (Although it is recommended you have it equipped when you are in Bikanel Island digging so you can avoid fiends and only fight the ones that ambush you when you dig at certain X's). A new enemy will also appear in random battles: Watchers. They only casting weak magic attacks, but throughout Chapter 3 and 4, they record your actions and report them to the Bosses you will encounter from now on. The Bosses will adjust their fighting style based on any action or ability you have used during a battle with a Watcher. Sometimes they even develop an immunity or ability and use it often to attack. To counter this, take the Watchers out first with regular physical attacks.
Travel down to the engine room to collect the chests for Phoenix Down x6, Ether x3, Remedy x5, and Hi-Potion x4. Then head up to the Cabin to rest and sell/buy items from Barkeep. When you are ready, you can either head on to the Hotspots to quickly get through the chapter or visit each place for completion points.