These three races were defined in Tall Tales of the Wee Folk from Basic DND for the old Mystara Setting. Here are my stats for using them in a 5e campaign. All background notes and flavor text are in the book, not here.
+1 Str, +1 Con, +1 Dex, Darkvision 45′, Advantage on any stealth action in the forest or woods, may ignore any movement penalties or chance of injury for moving through trees or bushes (may roll around on rose bushes safely, or run into a cactus and bounce off unharmed), has resistance to poison, gains advantage on saves vs poison, may use any weapons like a halfling could but does get the +1 damage for versatile weapons used two handed.
+2 Dex, +1 Int, limited flight (3 turns, must then spend 1 action to rest involuntarily), invisiblity to mortals at will, regardless of how a pixie becomes invisible attacking never causes invisibility to end
+2 Int, +1 Dex, Flight (same speed as move), invisible to mortals at will, may ritually cast magic even if not able to cast spells from a character class but only Curse and Confusion (initially requires 5 sprites working together, but takes less and less as power increases), may pick any one bard cantrip to cast exactly as if a bard of own level.
Invisibility to Mortals: A common power among true fey. Normal invisibility makes one invisible to everyone. This ability makes one invisible to anyone who is not of the Fey (Elf, some Half-Elves, Gnomes, Sprites, Brownies, Pixies, Sidhe, Imps, Dryads, Treants, etc). Some insects and animals are able to see through this invisibility as well. Even humans may sometimes perceive the faintest glimmer in the air, like the shimmering of air over pavement on a hot day, when a fairy is present. This especially occurs in the evening after sunset, when much of the light is near the violet end of the spectrum. Anything that detects invisible creatures will also work on creatures invisible to mortals. Dispel magic will force a faerie to become visible, but the faerie can always just re-activate the ability. It requires an action to become invisible and while invisible the faerie gains a bonus action each round that can only be used to maintain the effect. Attacking ends this invisibility (except for Pixies).