The name of this weapon varies between 'Avenger', 'Avenger's Edge' and 'Avengers'. アヴェンジャー [avenger] in Japanese.
Final Fantasy IV
Stats: ATK 90, ACC 85, STR +10, INT -10, MND -10, STA +10
Equip: Cecil, Kain
Buy: - (sell: 10,000 gil)
Drop: Behemoth
Treasure: Sylphs' cache
Other: makes wielder go Berserk
Final Fantasy IX

Stats: ATK 70
Equip: Amarant
Abilities: Counter, Demi Shock
Buy: 16,000 gil (sell: 8,000 gil)
Shop: Bran Bal (Moorock's mogshop), Daguerreo (weapon shop (disc 4))
Steal: Earth Guardian
Description: Powerful claws that can kill opponents with one hit
Type: H2H
Other: inflicts Death Blow with 15% probability with Add Status active
Other: as 'Avenger'
Final Fantasy XII
Stats: ATK 52, EVA 5
Range: 1, Charge time: 23, Combo chance: 7, Knockback chance: 0
Buy: 6,000 gil (sell: 3,000 gil)
Other: A 10% chance to Berserk target
Other: as 'Avenger'
Final Fantasy XIII-2
Stats: STR40, MAG26
Ability: Chain Bonus Lv 2, Accessory Ability Group: Strength+Magic
Buy: 1,520 gil, Begrimed Claw x3, Abominable Wing (sell: 760 gil)
Obtain: -
Description: ?
Final Fantasy XIV

Stats: DMG 133 (hq ATK +15), STR +7, INT +7, delay 3.4, DPS 39.12, Blunt
Equip: level 50 (required), PGL
Buy: - (sell: 6,018 gil)
Craft: BSM 55 - Fire Cluster, Earth Cluster, Flawless Avenger Grips, Darksteel Nugget, Rose Gold Nugget, Spruce Lumber
Type: Pugilist's Arm, Meld: Yes, Convert: Yes
Other: as 'Avengers'
Record Keeper

Avenger (XII)
Stats: ATK +19, ACC 89 (lv1), ? (lv5), ? (lv10), ? (lv15), ATK +45, ACC 89 (lv20)
Max Level: lv10 (initial), lv15 (first evolving), lv20 (second evolving)
Type: Dagger, Rarity: ★★★
Category: Equipment