These are the rewards that you can obtain by capturing fiends for the Monster Arena. Refer to the Monster Arena page for additional information about this massive side quest:

There are a number of rewards that you can unlock at the Monster Arena most notably by unlocking certain fiends of particular species types or that all come from the same location. There are a few one-off unlocks though which are also mentioned below. You can unlock the following three one-off items:

Nirvana
Re-open the Monster Arena by capturing one of each fiend that you can find in the Calm Lands. Note that you will need to have the Celestial Mirror in your possession in order to unlock and open the treasure chest (otherwise it will just sit there).

Blossom Crown
Capture one of each of the fiends that you can find in Mt. Gagazet.

Mars Sigil
Unlock 10 Area Conquest or Species Conquest monsters. This can be any combination of Area/Species conquests.

The rewards you can receive for completing Area Conquests, Species Conquests or Original Monsters are located below:

Area Conquest

Area	Fiend Unlocked	Reward
Besaid	Stratoavis	Stamina Tonic (x99)
Kilika	Malboro Menace	Poison Fang (x99)
Mi’ihen Highroad	Kottos	Soul Spring (x99)
Mushroom Rock Road	Coeurlregina	Candle of Life (x99)
Djose Highroad	Jormungand	Petrify Grenade (x99)
Thunder Plains	Cactuar King	Chocobo Wing (x99)
Macalania Woods	Espada	Shining Gem (x60)
Bikanel	Abyss Worm	Shadow Gem (x99)
Calm Lands	Chimerageist	Farplane Wind (x60)
Cavern of the Stolen Fayth	Don Tonberry	Silver Hourglass (x40)
Mt. Gagazet	Catoblepas	Blossom Crown
Inside Sin	Abaddon	Lunar Curtain (x99)
Omega Ruins	Vorban	Designer Wallet (x60)

Species Conquest

Species	Fiend Unlocked	Reward
Wolves/Lupine	Fenrir	Chocobo Feather (x99)
Reptiles	Ornitholestes	Stamina Spring (x99)
Birds	Pteryx	Mega Phoenix (x99)
Wasps	Hornet	Mana Tonic (x60)
Imps	Vidatu	Mana Spring (x99)
Eyes/Bats	One-Eye	Stamina Tablet (x60)
Flans	Jumbo Flan	Twin Stars (x60)
Elements	Nega Element	Star Curtain (x99)
Helm/Armored	Tanket	Gold Hourglass (x99)
Drakes	Fafnir	Purifying Salt (x99)
Fungii	Sleep Sprout	Healing Spring (x99)
Bombs	Bomb King	Turbo Ether (x60)
Ruminants	Juggernaut	Light Curtain (x99)
Iron Giants	Ironclad	Mana Tablet (x60)

Original

Requirement	Fiend Unlocked	Reward
2 Area Conquest	Earth Eater	Three Stars (x60)
2 Species Conquest	Greater Sphere	Supreme Gem (x60)
6 Area Conquest	Catastrophe	Door to Tomorrow (x99)
6 Species Conquest	Th’uban	Gambler’s Spirit (x99)
1 of each fiend (all)	Neslug	Winning Formula (x99)
5 of each fiend (all)	Ultima Buster	Dark Matter (x99)
2 underwater fiends (Mt. Gagazet)	Shinryu	Megalixirs (x30)
10 of every fiend	Nemesis	Master Sphere (x10)