How it works: When a Target performs a specific, actionable slight against you—such as mocking you for your height, stealing from you, insulting your draconic ancestry, or causing you harm, physically or emotionally—you can declare an unending grudge against them. The Dungeon Master (DM) and player should agree on a clear trigger and goal.

Once an unending grudge is active, you gain the following benefits against the target of your grudge:

• Heightened Senses: Your keen kobold senses sharpen to better track your quarry. You have advantage on any Wisdom (Perception) or Wisdom (Survival) checks made to find, follow, or track the Target.
• Tactical Focus: Your focus on getting revenge provides you with an uncanny tactical advantage against your specific foe. You have advantage on attack rolls against the target of your grudge when you are within 5 feet of them, so long as at least one of your allies is also within 10 feet of them. This is an evolution of your innate Pack Tactics, now focused by your personal vendetta.
• The Sweetest Revenge: You can perform an elaborate act of revenge that has been planned since the moment the grudge began. With the DM's permission, you can describe a specific, minor, or major act of retribution against your Target. This revenge must be the culmination of a series of deliberate acts of harassment and planning. 

Restrictions:

• A Grudge Never Ends (Unless Fulfilled): You can only hold one unending grudge at a time. The grudge ends only when you have successfully enacted your revenge against the Target.
• Focus, Not Rage: Your grudge is not a furious, uncontrolled rage. It is a cold, calculated fury that you use to plan your revenge carefully. You can take your time, sometimes years, to find the perfect moment.
• Not All Enemies are Grudges: A normal fight with a monster is not enough to trigger this feature. The slight must be personal and petty. You don't hold a grudge against an orc because it's an orc; you hold a grudge because that one specific orc tripped you as you were running away, and your pride has been wounded. 

How to use it in your game

• Long-Term Plot Hook: An unending grudge can become a defining character arc. Perhaps your kobold's grudge is what drives them to join an adventuring party in the first place, seeking a way to grow powerful enough to take on a foe that once wronged them.
• Petty Subplots: A grudge doesn't always need to be a major part of the main story. Your kobold could be on the lookout for a tavern owner who refused to serve them. The revenge could be as simple as an intricate series of embarrassing pranks that take a week to set up and execute.
• A Warning to Others: This feature is not only a boon for the player but also a narrative tool for the DM. Other players who slight the kobold should be wary; their characters may become the target of the grudge.