With the series running almost entirely non-stop alongside the video games, most Pokemon fans have probably seen at least an episode or two of the Pokemon TV anime. Ash's adventures through the Pokemon world to become the very best follows the core idea of the Pokemon games, but there are differences.
Among these differences are the way that Ash uses his Pokemon to battle. Most will remember Pikachu dominating almost anything the duo came across regardless of class advantages or disadvantages, and Ash sometimes carried over this fighting style to his other Pokemon, too.
An example of this was recently brought to light by Redditor Sticky_Robot, who was revisiting the original Pokemon anime. They point out that Ash was needlessly tough on his Kingler, which could have easily been a viable partner.
To be more specific, Ash caught a Krabby in the early days of the Pokemon show, but he had a full roster at the time, and it was automatically sent to Professor Oak's lab. After that, Ash never attempted to level or use his Krabby, until he made the puzzling choice to use Krabby in the midst of a major Pokemon League battle. This put the inexperienced and underleveled Pokemon up against an Exeggutor, which it has a type disadvantage against. Despite the disadvantage, Krabby managed to evolve into Kingler during the fight, and overcame Exeggutor.
Kingler managed to defeat two more Pokemon in another League battle, but was eventually knocked out by Arcanine, a Pokemon it should have a significant typing advantage against. The Pokemon was used in a fight once more in the Johto League arc of the show, and then never again in the two decades that have followed. It seems Kingler has been more or less abandoned to Oak's lab.
Redditor Sticky_Robot points out that this seems pretty unfair, considering that the underleveled 'baby crab' Krabby was able to perform so well at a major high-level battle. To be fair, the battle breaks several conventional rules of the way Pokemon fights work in the games; in addition to the typing advantage and disadvantages being seemingly ignored, Kingler uses eight different moves during its League fights. Ash's Pokemon often seem to ignore the realities of the Pokemon games and succeed based on willpower alone.
With hundreds of new Pokemon joining the series since the original Indigo Pokemon League, it's extremely unlikely that Ash's Kingler will ever be utilized again. Stranger things have happened in the Pokemon anime, of course, but even if Kingler does make an appearance, it's unlikely that it'll become a major part of Ash's team.
Source: Reddit