- You gain a +1 bonus to attack rolls you make with daggers.
- When you use a dagger, its damage die changes from a d4 to a d6. (This benefit has no effect if another feature has already improved the weapon’s die.)
- When you use the Attack action and attack with a one-handed weapon, you gain an extra attack with a dagger you are holding.
Notes: This is really just a first draft. I'm still not wild about the idea of feats giving bonuses to attacks rolls; that might encroach too much on 5e's bounded accuracy. It might also be not much of a big deal. Who knows?