I whipped up an oldschool D&D conversion of the 4e Avenger. No flavour text, but Google and all.
THE NEMESIS (Fighter Subclass)
Requirements: Lawful Alignment; Intelligence and Wisdom of 13, Dexterity of 15
Prime Requisite: Intelligence and Wisdom 15 or greater, +10% experience points
Weapons: All melee, crossbow, javelin and sling.
Armor: No armor or shield
Experience Points: As Paladin
Hit Points: As Fighter
Effective Armor Class as a Monk of the same level.
+1 on all saving throws.
At 3rd level gain the ability to turn and affect undead etc. as a Cleric two levels lower.
Find Traps, Move Silently, Hide in Shadows, Hear Noise and Climb Walls as a Thief of the same level.
-Once per combat you may select one enemy within 50' to be subject to your Nemesis Oath.
-If the enemy is slain or reduced to 0 hit points you may select another enemy to apply Nemesis Oath upon.
-If you are in melee range of the subject of your Nemesis Oath, and they are the only enemy adjacent to you, you gain a +4 to all melee attack rolls against them.
-If the subject of your Nemesis Oath willingly moves away from you, you gain +2 damage on all attacks against them until the end of your next turn.
-Once per combat you may allow one ally who is within 50' of you to make an attack with +4 on the to hit roll against the subject of your Nemesis Oath. This ability does not refresh if the subject of your Nemesis Oath is killed or reduced to 0 hit points.