Krokorok, as a Sandile, first appeared in A Line in the Sand!, where he immediately picked a fight with Lewis' Aipom. He was able to confuse Aipom with Dig, but was eventually knocked back by Focus Punch. Lewis then threw a Poké Ball, but Sandile broke free and fled the scene. At the end of the episode, Sandile began to follow Lewis.
Sandile next appeared in Seeing the Sights!, where Lewis discovered that he had followed him to Nimbasa City. Sandile had another battle with Lewis, this time taking on Oshawott. It was damaged by Oshawott's Water Gun, but still managed to deflect Lewis' Poké Ball and flee again.
It was later seen watching the battle between Lewis and N.
In the following episode, Sandile dug his way into the Nimbasa Gym, where it offered to be Lewis' third Pokémon in his battle against Elesa. It first battled Elesa's female Emolga and defeated it easily with Stone Edge. It then faced off against Zebstrika and took a lot of damage from Double Kick and Flame Charge. Using its Dig, Sandile made several holes in the battlefield, restricting Zebstrika's movement. He then managed to defeat Zebstrika with a combination of Snarl and Stone Edge.
After witnessing Lewis receiving his Bolt Badge, Sandile once again challenged him to a battle. He faced off against Lewis' Aipom once more and was weakened by Focus Punch. He then tried to bite through Lewis' Poké Ball, but it managed to activate inside Sandile's mouth, finally capturing it.
Sandile was the first Pokémon Lewis used in his battle against Burgh in The Art of Battle! He battled Burgh's Whirlipede and defeated it with Snarl. Lewis then recalled him and sent him out later to battle Burgh's Shelmet. Sandile, like Darumaka, ran into difficulty getting past Shelmet's defences. However, he managed to throw Shelmet into the air using Dig, causing Shelmet to panic and come out of its shell. Sandile then hit Shelmet with Stone Edge, defeating it. Next, Sandile battled against Burgh's Leavanny and was easily defeated by X-Scissor.
Sandile helped to protect the Floccesy Ranch from Team Plasma in Liberate the Ranch!
In A Celestial Rival Confrontation!, Sandile battled against Hugh's Lampent. He easily defeated it with Stone Edge, before being defeated by Servine.
Lewis used Sandile as his third Pokémon in his battle against Skyla in A Sky-High Gym Battle Royale! He faced Skyla's Swanna and was able to hold his own, despite the type disadvantage. However, he was eventually taken out by a super-effective Bubble Beam.
In Getting Up on the Wrong Side of Evolution!, Sandile buried itself in the sand while the group were relaxing on the beach in Undella Town. When Lewis attempted to discover what was wrong, Sandile suddenly evolved into Krokorok. Krokorok immediately began to pick fights with the other Pokémon, causing Lewis to request that he and Nate have a battle to try and calm Krokorok down. During the battle, Krokorok adamantly refused to listen to Lewis' commands and battled Magneton as he wanted, demonstrating that he had learnt Earth Power. While Krokorok defeated Magneton, he was unsatisfied and began to battle Bianca's Vanillish instead. Eventually, Duosion used Confuse Ray to stop Krokorok, allowing Lewis to recall it, concerned about what had happened to his friend.
In Dangerous Rival Confrontation!, Lewis decided to use Krokorok in a one-on-one battle against Hugh's Absol. Once again, Krokorok refused to listen to Lewis' commands and was defeated as a result. Hugh told Lewis that Krokorok no longer respected Lewis, as he felt that Lewis was holding him back from his true potential.
In the following episode, Lewis sought to re-connect with Krokorok and so went into the mountains with it to bond, leaving his other Pokémon at the Pokémon Centre. The group were then attacked by a wild Krookodile, who Krokorok immediately attempted to battle. The battle escalated, scattering the group and causing Krokorok to fall off a cliff into a lake below, with Lewis leaping after him. Taking Krokorok to a cave hidden behind a waterfall, Lewis worked to get his health up, causing Krokorok to begin to change his views of Lewis. Deciding to help Krokorok get even with Krookodile, Lewis began teaching it how to use Iron Tail. After training throughout the night, Krokorok finally mastered it, regaining his respect for Lewis in the process.
The following day, Lewis and Krokorok encountered the Krookodile again and challenged it to a rematch. Krokorok battled alongside his Trainer for the first time since it evolved and managed to defeat Krookodile with its new Iron Tail, sending it running away. Krokorok and Lewis then shook hands, happy at their reunion.
Krokorok was Lewis' third Pokémon in his Gym Battle with Roxie in Take the Battle Stage! He battled against Roxie's Muk and defeated it with Earth Power. He then faced off against Roxie's powerful Koffing and lost, despite holding the type advantage.
Krokorok was used in several battles during the Unova League. He battled against Amanda's Emboar in Trick Room of Terror!, where he fought hard against the Mega Fire Pig Pokémon. Eventually, the battle ended in a draw. He also faced off against a Maractus in In the Maractus! and defeated it with Iron Tail.
In A Full-Strength Rival Battle!, Krokorok was Lewis' first Pokémon in his battle against Hugh. Krokorok first battled Hugh's Zebstrika and won. He was then recalled and later battled Unfezant, but was defeated.
Krokorok was Lewis' final Pokémon during his battle against Tunja in A Fierce Clash of Titans! He battled against Tunja's overwhelmingly powerful Metagross. Despite holding up better than some of Lewis' other Pokémon, Krokorok still took heavy damage from Metagross' attacks without dealing much damage in return. A powerful Meteor Mash smashed Krokorok into the ground. However, the critical damage sustained from the attack activated Krokorok's Anger Point Ability, boosting its Attack to the maximum. With his new power, Krokorok was able to deal major damage to Metagross, pushing it to the edge of defeat. However, the damage Krokorok had sustained became too much and he was unable to stand up to another Meteor Mash, causing Lewis to lose the battle and be eliminated from the Unova League.
Lewis left Krokorok at Professor Juniper's Laboratory when he decided to go to Sinnoh.
As a Sandile, Krokorok was shown to be quite the unruly Pokémon, often causing trouble for those around it and taking delight when those people get frustrated with his antics. He was also shown to be fairly mischievous, twice tricking Lewis into thinking he had captured it before escaping and laughing. Despite this, he is shown to care for others, as seen in A Fashionable Gym Battle!, where it decided to help Lewis in his Gym battle of his own accord.
Krokorok is shown to take great pride in his battling skills, as shown in A Celestial Rival Confrontation!, where he gloated to Hugh about his easy victory over Lampent.
Upon evolving, Krokorok became much stronger, but also developed an aggressive personality and wished to constantly prove his strength. He would often attack other Pokémon, even those belonging to the group, to try and assert his dominance over them. He also flat-out refused to listen to Lewis' commands. However, in The Tyranny of Krookodile!, after Lewis healed him and successfully taught him Iron Tail, Krokorok began to regain his respect for the Trainer and happily battled alongside him against Krookodile. He also shook hands with Lewis after the battle, reaffirming their new bond.
Since losing to Krookodile in The Tyranny of Krookodile!, Krokorok has harboured an extreme hatred of his evolved form, going as far as to come out of his Poké Ball on his own to challenge one that may be nearby.