A unique ancestry
Fast thinker: You get advantage on initiative check.
Easy going: after you complete a rest you gain a Luck token.
Adding new ancestry won’t be easy. We got a limited pool a features to use. A luck token is not a perfect niche, since the DM can allow them, the Bless spell too, but it’s an honest take for home brewer.Oooh...I think I like that! It's a simpler version of what I proposed earlier (reroll spell and thievery checks once a day) and it fits the idea of gnomes being lucky.
Speaking with burrowing animals always seems too limited to stand next to real features, but speaking to small or smaller critters is juicy.Some potential features for the gnomes:
- Can move into tiny, X-wide openings.
- Can mimic any sounds without moving their lips
- Can work on mundane chores while resting without interrupting the rest.
- Speak with burrowing animals.
- Can enchant tools and object to use them at distance.
- Have advantage to resist mind-affecting spells.
- +2 to spellcasting roll while hidden.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.