Trophy items is a recurring set of items in the series. They are generally of little to no value in terms of gameplay, as they don't do anything on their own and are not usually used for anything. They exist to signify the player has overcome some of the most difficult trials in the game, usually by defeating a superboss. Trophy items generally show up the most with the superboss Omega, in the form of the Omega Badge. Trophy items were common before achievement systems were introduced.
The Omega Badge is acquired after defeating the superboss Omega in the Interdimensional Rift, while the Dragon Seal is acquired after defeating the superboss Shinryu. An additional item, the Medal of Smiting, is acquired after completing the Cloister of the Dead in the Game Boy Advance and succeeding remakes.
There are multiple unusable items, which are won as prizes at the Battle Square. Unlike most trophy items, they are more for comedy than for showing off. The Tissue, for instance, drops after almost every battle as a "consolation prize". For beating the Special Match, the player can win the Masamune Blade (a copy of Sephiroth's sword, not an actual weapon), the Combat Diary and Gambler written by Dio, and the Autograph. The Super Sweeper, Masamune Blade and 1/35 soldier can also be won at the Speed Square.
The items dropped from the superbosses Emerald Weapon and Ruby Weapon actually serve a purpose, and thus are not just for show. Earth Harp from Emerald Weapon yields a set of Master Materia, and the Desert Rose Ruby Weapon drops yields a gold chocobo, respectively, if presented to the Kalm traveler.
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While not an actual item, the Proof of Omega is obtained after defeating the superboss Omega Weapon in Ultimecia Castle, and will appear in the Tutorial section of the menu. Another type of menu trophy is the star that appears next to the Triple Triad section after the player has held every card.
The Strategy Guide is obtained after defeating the superboss Ozma at the Chocobo's Air Garden. Rank S Award is obtained from Gilgamesh when the player attains the highest Treasure Hunter Rank. The Southern Tropical Outfits could also be seen as trophy items, as although usable as armor they have no stats, are are akin to joke equipment.
The Mark of Conquest is obtained by beating Nemesis in the Monster Arena. To unlock Nemesis, the player must capture 10 of each fiend found in Spira and defeat all other Original Species, Area Conquest, and Species Conquest monsters at least once.
Centurio Hero's Badge is awarded for reaching the highest rank in Clan Centurio. To get the highest rank, the player must fill out the Sky Pirate's Den, complete all 45 hunts and have a million clan points.
Although the Wyrmhero Blade is usable as a weapon, it is effectively more of a trophy item due to the player needing to have slain the game's superbosses to get it, and the weapon being slow to use albeit with high stats and combos. The trophy for completing the fishing minigame is also needed to make it.
The penultimate boss drops the Infernian Shards key item that doesn't have a known usefulness.