Sandy first appeared in the first episode of the Where Are You Going, Eevee? shorts. It was exploring in the streets of a town, only to run foul of a Houndour when it stole its food. It managed to escape Houndour, and after seeing the ocean, it set sail on a boat. It reappeared in the second episode of the segment, where it fell off the boat. However, it was rescued by a Mantine, which took Eevee on its back so it could bring it to the shore.
In the third episode of the segment, Eevee and Mantine decided to try Mantine Surfing on a nearby wave. While it initially kept getting knocked off whenever Mantine did a flip, Eevee eventually learned how to time its jumps with Mantine's flips, allowing it to stay on Mantine's back. At the end of the fourth episode of the segment, Eevee arrived in Alola, where it said its farewells to Mantine and proceeded to explore the island. It first chased after a Wimpod before eating some Nanab Berries.
In the fifth episode of the segment, Eevee encountered Ash and his classmates' Pokémon for the first time and befriended them. In the sixth episode, Eevee played with them at the beach and even helped knock some Berries down from a tree to share with them. At sunset, the other Pokémon returned to their respective Trainers, while Eevee sadly returned to its impromptu home under a tree trunk to sleep.
In We Know Where You're Going, Eevee!, Eevee wanted to see its new friends again, so it wandered around Hau'oli City, and eventually ended up getting chased by an AlolanPersian. After being rescued by Lana's Popplio, both ended up falling into a river and washed up on the Hau'oli City Beachfront, where they encountered Team Skull GruntsTupp, Rapp, and Zipp. Tupp and Rapp began fighting over Eevee, as the former wanted Eevee to make him popular with girls while the latter found Eevee to be cute. They were stopped when Lana and her friends arrived. With its newly-learned Surf, Popplio created a platform of water for Eevee to jump on, allowing it to use a powerful Double-Edge and send the Team Skull Grunts blasting off. After some encouragement from Ash and Mallow, Lana asked Eevee if it wanted to join her team, which it happily accepted. Eevee was named Sandy and caught in a Dive Ball. After returning home and introducing Sandy to her family, Lana gave Sandy a haircut, cutting its long bangs to a shorter length resembling her own hair. This got rid of the hair that kept blocking its vision, much to Sandy's pleasure.
Sandy and Lana
In SM117, Sandy joined Lana and her classmates during their two-day trip to Malie City. Soon after their arrival, Sandy started curiously exploring its surroundings and even absentmindedly tried to cross a road, requiring Shaymin to save it from getting hit by a car. During the group's visit to Malie Garden, Sandy let Ash's Meltan ride on its back. Later, when Mallow's hair ornament was blown away by the wind and Shaymin chased after it, Sandy and Meltan followed it. After Sandy and Meltan helped Shaymin recover the hair ornament, the three Pokémon were imprisoned by Team Rocket. The metal cage was too sturdy for Sandy's Tackle to break through, but thanks to Meltan's ability to eat metal, the three Pokémon were able to get out. Team Rocket then sent out their Pokémon, and Sandy started battling James's Mareanie, but wound up being poisoned by her Sludge Bomb. However, Lana, Ash, and Mallow intervened, while Shaymin healed Sandy of its poison. Following this, Meltan and Sandy were able to defeat Mareanie with a combination of Headbutt and Double-Edge.
Sandy is adventurous and gluttonous, traits that often got it into trouble, such as when it ate a Houndour's food without permission, angering the Houndour into chasing it off. Sandy is also extremely playful, like when it enjoyed falling into the ocean after falling off Mantine when it was Mantine Surfing. However, it is also easily scared as well, such as when it ran from a Houndour and later when it found itself lost at sea.
Sandy is particularly playful towards new Pokémon, but prone to roughhousing in the process, greeting friends old and new with a hearty Tackle. As a result, it tends to get into trouble. In the fourth episode of the segment, it chased after a Wimpod despite it actually being scared. In the fifth episode of the segment, Sandy cuddled a Pyukumuku, inadvertently angering it into attacking.
Sandy and Primarina, while it was a Popplio, quickly became best friends after meeting each other, and Sandy appears to look up to it like an older sibling. In Evolving Research!, it was seen enthusiastically mimicking Popplio as it was training with Ida's Primarina, singing along with the master and its disciple. It even became friends with the Pokémon owned by its Trainer's friends. Sandy quickly became loyal to Lana and bonded with her right away, after she helped protect it from Team Skull.
Sandy cares for its friends even in dire situations, such as changing to a slow pace so that it can run beside Popplio as they ran away from a Madame's Persian, Pershie. Also, when its friend Mantine and the Poké Ride Mantine were captured by Team Rocket in Alola, Alola!, it was the first to rush in and help. In That's Some Spicy Island Research!, Sandy was revealed to love the taste of Poni Islanddaikon. Sandy also loves the ocean and enjoys playing in it no matter what the activity. Sandy is very curious and absentminded, to the point where it was almost hit by a car in SM117 while attempting to cross a road, as well as rushing in the middle of an Eevee procession and mistaking a Swablu statue for the actual Pokémon.