The first thing that catches the eye is the razor thin blade of the Flesh Seeker. Allowing the sword to slip between armor, the blade is perfectly balanced to allow greater control enabling a master swordsman to penetrate weaknesses in even the most armored of foes. In low fantasy settings, the Flesh Seeker can simply be a masterwork sword with a bonus to attack rolls between 1-3 depending on how strong the DM wants the item to be. However, once the swordsman identifies a weak point in their enemies armor, by landing a hit, then he/she knows right where to strike. This provides an additional +1 to the attack roll on the next attack, or allows advantage if you are playing D&D 5e. This is also the base mechanic, and further affects can be applied to fit your game or player theme. Another option is to lean into the magic aspect of Flesh Seeker weapon.
If you want to embrace the magic element, then maintain the same affects but describe the blade’s thirst for flesh. After landing the first hit, say something like “As blood flows down the edge of the blade, you feel a warm energy as the sword awakens in your hands, it desires more!” The flavor text in the D&D 4th edition books also state that this sword can bypass magical defenses. To me, this doesn’t quite fit thematically with the item. So, I would do away with that section and double down on the blood-thirst aspect described in the text. An interesting concept to explore could be if this weapon has any affect on the character? If a barbarian utilizes this sword in a rage, well… I could imagine that character falling victim to an intense blood-lust. Now, this may simply be a role-play element rather than a mechanical rule-set for the sword. I’m hesitant to put negative affects on items without a strong narrative reason. Also, keep in mind that you can customize this weapon for your players. The original concept was more of a sleek looking blade, but one could take these core mechanics to craft an ax or anything else that fits your player’s theme. Lean into whatever feels right for that weapon type. For Example:
- Duel Short-Swords: These blades are a pair, and are constantly competing with one another. When one sword hits, than the other gets a +1 (or advantage) on its next attack.
- War-hammer: This weapon loves to cave skulls. When you kill an opponent by bashing its skull (which should be always!), you gain a +1 (or advantage) on your next attack, and add a 1d12 to its damage if the hit is successful.
- Great Ax: Cleaving its enemies with gashing wounds, you gain a +1 (or advantage) on your next attack, and if successful, that attack does max damage. (even if crit!)
Again, these are just some ideas to flavor the Flesh Seeker weapon to the player/character you wish to reward. That’s the thing about these magic items, they should always be rewards, and the players should feel powerful wielding them. Obviously, as the DM, you still need to balance the game, but because the player needs to first land a successful strike, and then make a successful follow-up, you have some room to allow a powerful affect. The stars won’t always align, however, the player will still get the additional +1 a fair amount, and when the player does face a group of low AC foes, well, they will feel like the harbinger of death!