Nemesis is a superboss in Final Fantasy X created by the old man who runs the Monster Arena in the Calm Lands. Nemesis is an Original Creation monster and a color variation of Ultima Weapon. Often nicknamed "Omega Gold", it is the most durable and most challenging enemy in the original versions of the game (Penance and arguably some of the Dark Aeons in the PAL and International versions of the game are harder), with 10,000,000 Hit Points and an array of spells and attacks that can instantly kill even the highest-level, best-equipped parties.
To unlock this battle, the player has to capture ten of every fiend (that can be captured) and defeat all the other creations in the Monster Arena. Defeating Nemesis in the HD Remaster version earns the trophy Overcoming The Nemesis.
Special damage, including Overdrives and items, will cause Nemesis to counter with Ultima. His Ethereal Cannon is a non-elemental magic-based attack against one character, and Ultra Spark will inflict many status ailments: Poison, Curse, Slow and Power Break on the party. Moreover, Ultra Spark inflicts the kind of Power Break that can penetrate through immunity, effectively weakening an Aeon's Strength. Nemesis's ultimate attack is Armageddon, which hits all characters for 99,999 damage. The latter is graphically identical to Omega Weapon's Nova.
Nemesis's attack pattern is semi-predictable. He will alternate between Ethereal Cannon and Ultra Spark, though he may use normal physical attacks in-between. He is guaranteed to use at least one physical after Ultra Spark before the next Ethereal Cannon. Use of a random physical attack gives Nemesis 3 points towards Armageddon, while any other attack (including the obligatory physical attack in-between Ultra Spark and Ethereal Cannon) gives him 2; when he reaches 19 points he uses Armageddon on his next turn. Use of Armageddon delays, rather than replaces, the next attack in his pattern.
If a player missed Kimahri's Nova Ronso Rage from Omega Weapon, it can be acquired from Nemesis. Despite Nemesis's rare steals (Lv. 4 Key Sphere, Warp Sphere), stealing from it is not exactly straightforward, as it will counter with Ultima, doing extreme damage to the whole party. Mug does not cause it to counterattack.
For an easy win, the player should use three party members with fully powered Celestial Weapons, not including Yuna. The party should use nothing but Quick Hit to deal massive damage before Nemesis gets a chance to act. When his turn is about to come up the player should switch in Yuna and summon.
The aeon will get in one or two attacks before being killed, at which point the original party can return and resume Quick Hit. Nemesis will run out of HP long before Yuna runs out of aeons. This strategy guarantees a win without the party taking a single HP of damage. Shell can be used to reduce the damage of Ethereal Cannon and Ultima, and Protect can be used to reduce the damage of Nemesis's physical attack. However, neither of them will affect Ultra Spark, which can only be reduced via an increased Defense stat (including via Cheer) or an aeon using Shield.
This strategy is still viable but no longer as effective in the international edition and HD remaster of the game, because Quick Hit no longer removes as much delay as the original NA/JP version. In this case, use of Auto-Life becomes practically mandatory to survive Ultra Spark and Armageddon. Having a supply of Megalixirs on hand can be useful to quickly heal damage. If the player enters with the Magus Sisters and Anima's Overdrive bars maxed, or Yuna's for Grand Summon, then these can also be used to deal some heavy damage to Nemesis before it takes out the aeon.
Following defeat, Nemesis will drop weapons with Break Damage Limit or armor with Break HP Limit abilities and two or three empty expansion slots. Its equipment drops provide a 6% critical hit chance bonus instead of the usual 3% (this is relevant to weapons and armors, but only to attacks that deal physical damage).
Once Nemesis is defeated the player will receive the coveted key item, Mark of Conquest. Despite the bragging rights that come along with such an item, Nemesis can be fought an unlimited amount of times provided the player has enough gil.
Nemesis means something a person cannot conquer, or an opponent whom a person cannot best. It can also mean an agent or act of retribution or punishment. It originates from Greek némesis meaning "a dealing out", verbid of némein "to dispense (justice)".
The Japanese name for Nemesis, (すべてを超えし者, Subete Wo Koeshimono?) means "he who hath transcended/conquered all". His name is Il Supremo in Italian, meaning "the supreme", Summum in Spanish, which means "the top, the max" in Latin, Être Suprême, lit: Supreme One, in French, and Deus in German, which is Latin for "god".