Sidequest

Sidequests are completely optional, mostly non-storyline objectives the player can undertake throughout the game, and has been predominant throughout the series. Sidequests can range from something as little as an errand or finding an item to something as big as traveling over the world for many various objectives or fighting superbosses. Several sidequests often involve getting powerful magic, summons, or equipment that would otherwise make the game extremely easy to complete.

Final Fantasy IV

 * Odin - The player may challenge Odin in Baron once they have gone to the Moon the first time. After defeating Odin in battle, the player will receive him as a summon.
 * Feymarch - Isolated on an island in magma in the Underworld. It is where the player may obtain several powerful equipment as well as the Avenger sword, and can challenge both Asura and Leviathan to a battle to obtain them as optional summons.
 * Lair of the Father - Accessed once the player can go to the moon. The player can engage Bahamut here once they have obtained Leviathan to try and obtain him as a summon.
 * Adamant Isle Grotto - Near Mythril Village, and the site of the Pink Puff Tail sidequest (and other tails in the DS version). Bringing a Pink Puff Tail will grant an Adamant Armor to the player. Bringing the Rat Tail will grant the player an Adamantite, which the player can use to obtain the Excalibur.
 * Sylph Cave - Found in the northwestern part of the underworld. The player can obtain the optional summon Sylph after they talk to Yang, return to Fabul and get the Pan, and then use the Pan on Yang. Returning the Pan to Fabul will also yield the Knife. This must be done before going to the moon for the first time.
 * Lunar Ruins - Several optional bosses can be fought here for various powerful equipment, such as Ragnarok and Ribbon. The bosses include Dark Bahamut, Ogopogo, Lunasaur, Plague Horror, and White Dragon.