The Dark Aeons is a good challenge in Final Fantasy X. Think the game is too easy try them out before you say the game is too easy. Personally for me I use "Yojimbo" Overdrive, Zanmato to finish them off. But to beat the the hard way there only 1 advice. Get your characters to max status and with the best weapons, overdrive, armour and accessories. Or get the cheats to help you out if you want to be so called cheaters.

Dark Valefor
Location: Besaid Island - Temple
HP: 800 000
AP: 10 000 - Overkill: 15 000
Stats
Strength: 148
Defense: 120
Magic: 186
Magic Defense: 220
Agility: 105
Luck: 48
Evasion: 10
Accuracy: 250
Elemental Immume to: All half damage
Other
Spoils
Normal: Dark Matter 1 or 2
Rare: Master Sphere 1 or 2
Weapons: First Strike, Firestrike, Lightningstrike, Waterstrike, Icestrike, Break Damage Limit
Armor: Auto-regen, Ribbon, Break HP Limit

How to defeat: Very Easy, a perfect attack reel will kill him. Auto-Life to play safe. Make sure your every attack of Wakka is 99999

Dark Ifrit
Location: Entrance to destroyed Al Bhed Home
HP: 1 400 000
AP: 20 000 - Overkill: 30 000
Stats
Strength: 220
Defense: 173
Magic: 177
Magic Defense: 163
Agility: 124
Luck: 27
Evasion: 8
Accuracy: 230
Elemental Immume to: Absorbs fire, immune to lightning and water, half damage to ice
Other
Spoils
Normal: Dark Matter 1 or 2
Rare: Master Sphere 1 or 2
Weapons: Break Damage Limit, Firestrike
Armor: Fire Eater, Ribbon, Break HP Limit

How to defeat: Easy, attack reel and blitz ace will kill him. Use aeons when his overdrive is full to block. Auto-life recommended. Make sure again all attacks are 99999.

Dark Ixion
Location: Thunder Plains - Go near the monk
HP: 1 200 000
AP: 20 000 - Overkill: 30 000
Stats
Strength: 176
Defense: 220
Magic: 133
Magic Defense: 188
Agility: 180
Luck: 36
Evasion: 0
Accuracy: 250
Immume to: Aborbs lightning, immune to fire and ice, half damage to water
Other
Spoils
Normal: Dark Matter 1 or 2
Rare: Master Sphere 1 or 2
Weapons: Break Damage Limit, Lightningstrike
Armor: Lightning Eater, Ribbon, Break HP Limit
NOTE: You have to fight this guy 2 times, remember that.

How to defeat: Easy, as long as you have sleepproof, or better still ribbon, and
auto-phoenix. This is bacause his normal attacks cause sleep in addition to
full break. You need to fight him twice.The first time you fight him,he will
only cast Aerospark when his overdrive is fully charged. Beware of his Thor's
Hammer overdrive during the second fight. Use Aeons to block if your HP is low,
and as his second incarnation is slower, quick hits should take him down before
he has a chance to use it. Play safe, have auto life and your damage deal is 99999.

Dark Shiva
Location: Macalania Temple - Entrance
HP: 1 100 000
AP: 20 000 - Overkill: 30 000
Stats
Strength: 173
Defense: 163
Magic: 244
Magic Defense: 255
Agility: 255
Luck: 73
Evasion: 0
Accuracy: 250
Immume to: Absorbs ice, immune to lightning and water, half damage to fire
Other
Spoils
Normal: Dark Matter 1 or 2
Rare: Master Sphere 1 or 2
Weapons: Break Damage Limit, Icestrike
Armor: Ice Eater, Ribbon, Break HP Limit

How to defeat: Max agility is a must otherwise she will kill you before you have a
chance to attack. Use Aim several times to be able to hit her. Beware her
Heavenly Strike which is instant kill even with ribbon armor, rely on Auto
Phoenix. Use Aeons to block her overdrive as usual. Other than that she is not
so hard.

Dark Bahamut
Location: Where you fought Yunalesca in Zanarkand Ruins
HP: 4 000 000
AP: 30 000 - Overkill: 40 000
Stats
Strength: 245
Defense: 234
Magic: 222
Magic Defense: 233
Agility: 255
Luck: 102
Evasion: 0
Accuracy: 255
Other
Spoils
Normal: Dark Matter 1 or 2
Rare: Master Sphere 1 or 2
Weapons: 1 MP Cost, Double AP, Double Drive, Break Damage Limit
Armor: Auto-Protect, Ribbon, Break HP Limit

How to defeat: This battle is tough, Just pray for Zanmato. ^_^

Dark Yojimbo
Location: Cavern of the Stolen Fayth
HP: 1 600 000
AP: 8 000 - Overkill: 10 000
Stats
Strength: 244
Defense: 210
Magic: 131
Magic Defense: 144
Agility: 243
Luck: 114
Evasion: 0
Accuracy: 255
Other
Spoils
Normal: Dark Matter 1 or 2
Rare: Master Sphere 1 or 2
Weapons: Counterattack, Magic Counter, OD->AP, Break Damage Limit
Armor: Curseproof, Ribbon, Break HP Limit
NOTE: You have to fight this guy 5 times, remember that.

Dark Anima
Location: Mount Gagazet, redo the challenge in which Wakka had to throw a ball at the revolving thing then teleport back to the entrance to Mount Gagazet and Dark Anima will be there waiting for you.
HP: 8 000 000
AP: 30 000 - Overkill: 40 000
Stats
Strength: 155
Defense: 230
Magic: 255
Magic Defense: 255
Agility: 183
Luck: 85
Evasion: 0
Accuracy: 255
Immume to: Absorbs everything
Other
Spoils
Normal: Dark Matter 1 or 2
Rare: Master Sphere 1 or 2
Weapons: Deathstrike, 1 MP Cost, Triple AP, Break Damage Limit
Armor: Deathproof, Break HP Limit, Ribbon

How to defeat: This battle is tough, Just pray for Zanmato. ^_^

Dark Cindy
Location: Mushroom Rock, from exit of Mi'ihen Highroad walk until you encounter two summoners.
HP: 3 000 000
AP: 10 000 - Overkill: 12 000
Stats
Strength: 175
Defense: 233
Magic: 171
Magic Defense: 105
Agility: 185
Luck: 50
Evasion: 0
Accuracy: 255
Other
Spoils
Normal: Dark Matter 1 or 2
Rare: Master Sphere 1 or 2
Weapons: Alchemy, Triple Drive, Gillionaire, Break Damage Limit
Armor: Auto-Phoenix, Break HP Limit, Ribbon

Dark Sandy
HP: 2 500 000
AP: 10 000 - Overkill: 12 000
Stats
Strength: 186
Defense: 201
Magic: 207
Magic Defense: 168
Agility: 201
Luck: 80
Evasion: 100
Accuracy: 255
Immume to:
Other
Spoils
Normal: Dark Matter 1 or 2
Rare: Master Sphere 1 or 2
Weapons: Evade and Counter, Magic Counter, Triple OD, Break Damage Limit
Armor: Auto-Shell, Break HP Limit, Ribbon

Dark Mindy
HP: 2 000 000
AP: 10 000 - Overkill: 12 000
Stats
Strength: 148
Defense: 187
Magic: 248
Magic Defense: 132
Agility: 233
Luck: 130
Evasion: 240
Accuracy: 255
Other
Spoils
Normal: Dark Matter 1 or 2
Rare: Master Sphere 1 or 2
Weapons: Magic Booster, 1 MP Cost, Triple Drive, Break Damage Limit
Armor: Auto-Haste, Break HP Limit, Ribbon