PHB, Homebrew, MotM
Cisum halflings are a small, but practical folk. Not prone to fancy things or a fancy life, they are often found in simple dwellings in communities of their own kind. Most halflings are quite cheery and welcoming, with strong bonds to family and community. Those that live among the other races can blend in easily, due to their size. However, their fierce loyalty and strong work ethic make them excellent hires for any knowing businessperson. Halfings among the islands tend to favor fishing over the farming life of their mainland kin.
If playing with achievements and milestones, choosing this race at character creation grants the player the achievement "Short People."
Lucky. When you roll a 1 on the d20 for an attack roll, ability check, or saving throw, you can reroll the die and must take the new roll.
Brave. You have advantage on saving throws against being frightened.
Halfling Nimbleness. You can move through the space of any creature that is of a size larger than yours.
Subrace. The three main kinds of halfling, lightfoot, stout, and waveskimmer, are more like closely related families than true subraces. Choose one of these subraces.
As a lightfoot halfling, you can easily hide from notice, even using other people as cover. You're inclined to be affable and get along well with others. Lightfoots are more prone to wanderlust than other halflings, and often dwell alongside other races or take up a nomadic life.
Ability Score Increase. Your Charisma score increases by 1.
Naturally Stealthy. You can attempt to hide even when you are obscured only by a creature that is at least one size larger than you.
As a stout halfling, you're hardier than average and have some resistance to poison. Some say that stouts have dwarven blood.
Ability Score Increase. Your Constitution score increases by 1.
Stout Resilience. You have advantage on saving throws against poison, and you have resistance against poison damage.
As a waveskimmer halfling, you spend most of your time in, on, or near the sea or ocean. You're a bit leaner than other halflings, and fair better as a swimmer.
Ability Score Increase. Your Wisdom score increases by 1.
Big Wave, Small Swimmer. You gain a swim speed of 30 feet, and have advantage on Intelligence (Perception) and Wisdom (Nature) skill checks when they pertain to the ocean.