It's pretty rare for a Pokémon to originate in the Pokémon anime as opposed to the games, and even those introduced in the anime first are typically just previews for the game. There's one major exception, however, and that is the Ash-Greninja form.

Ash-Greninja was a special form created for the anime, giving Ash something analagous to a Mega Evolution through an anime-original concept known as the "Bond Phenomenon." Though Ash-Greninja was introduced during the XY anime, it was never actually usable in the X and Y games. Ash-Greninja made its first appearance in the games with the release of Sun and Moon, and was made available to those who completed a demo of the game before its release. This, of course, is when the Ash-Greninja form immediately became something of a problem, as its power was too great.

How Ash-Greninja Got Banned in Generation 7

Ash's Special Form for Greninja Was Just Too Strong

The way the Ash-Greninja form works in the games is a bit different from in the anime. In the anime, Ash and Greninja were bonded telepathically, and Ash suffered the same injuries that Greninja received. In the games, after defeating an opponent, Greninja with the Battle Bond ability will transform into Ash-Greninja, an alternate form with a higher stat total than an ordinary Greninja. Additionally, its Water Shuriken attack will be boosted from 15 to 20, and will always strike three times, whereas before it only had a chance of striking that many times.

That isn't all that Ash-Greninja gets, however. Since it is like a Mega, but not technically a Mega, it wasn't restricted by the rule of only one Mega per team. Additionally, because its ability is so specific to Greninja, the usual tricks to eliminate an opponent's ability, like the attack Simple Beam or the ability Mummy, won't work. Even a Ditto can't use Battle Bond to transform. This made it a fairly safe choice when dealing with such opponents, shutting down one of their primary avenues of offense.

Additionally, its limited availability gave those who had it a major advantage over those who didn't. In the interest of fairness, Ash-Greninja (or more specifically, Greninja with the ability Battle Bond), was banned from most official tournaments during the seventh generation. Greninja didn't appear in Sword and Shield at all, so it was moot at that point, and when it came back in Scarlet and Violet's DLC, Battle Bond had been reworked to no longer have the transformation effect or the Water Shuriken improvement, instead raising all its offensive stats by one stage (a 50% increase). Thus, Ash-Greninja was retconned out of the games.

Ash-Greninja Wasn't a Unique Circumstance

The Anime Has Influenced the Games in Other Ways

As something of an early adopter bonus, Ash-Greninja was likely never meant to stick around, unfortunately. Aside from the aforementioned Spiky-Eared Pichu, which was also an anime tie-in, Ash-Greninja was one of the biggest cases of the anime influencing the games, but interestingly, it wasn't the only case in Alola. Also introduced was the special event-only form "Pikachu in a Partner's Cap," which featured Pikachu wearing Ash's various hats from over the years. These Pikachu even had a special Z-move that was inspired by the anime, 10,000,000 Volt Thunderbolt.

In a bizarre twist, however, while Ash-Greninja was banned, the Partner Cap Pikachu were never banned, despite being just as unattainable. Weirder still, the Partner Cap Pikachu was allowed into Sword and Shield, and are still ed by the games to this day. Sword and Shield even added a new Partner Cap, the Journeys cap, giving Pikachu a total of 8 hat-wearing alternate forms. Why these Pikachu that honor Ash's journey get to remain in the Pokémon games, but Ash-Greninja wasn't, remains a complete and utter mystery.

Greninja certainly had the popularity, and difficult forms like this have generally become more available in the future (Dusk-form Lycanroc, for example, was originally event-exclusive, but became an ordinary spawn in Scarlet and Violet). There's no reason that Game Freak couldn't have lifted the breeding restriction, for example, or made Battle Bond a rare ability, like Rockruff's Own Tempo. Ash-Greninja could've lived on, so why didn't it?

Pokémon Removed What Made Greninja Special

The Series' Retcon of Ash-Greninja Was a Mistake

As a result, Ash-Greninja is only a usable Pokémon in the 7th generation games, something that's extremely disappointing for collectors and anime enthusiasts alike. With the 3DS services having shut down, it's impossible to get one if you don't already have one, or if you sent yours to Pokémon Home. Greninja with Battle Bond are also unable to breed, so one can't obtain more of them that way, either. It s the ranks of Pokémon like Spiky-Eared Pichu and Cosplay Pikachu, being trapped in one particular game and unable to be used in later versions.

This purge of Ash-Greninja wasn't just restricted to the games, either. In Journeys, there are some flashbacks to the XY anime which were reanimated to remove Ash-Greninja and replace his appearance with that of an ordinary Greninja. It's truly a bizarre move, as if the entire Pokémon franchise would rather we all forget that Ash-Greninja ever existed, despite it being such a huge plot element of the XY anime, which remains one of the most popular seasons. And besides all that, Ash-Greninja does look cool, so it's always sad to see something interesting go away like this.

Ultimately, the video game implementation of Ash-Greninja was just a little too powerful to be allowed to be freely wielded, especially when only certain people were allowed to have one. This resulted in the form being banned from competition in the only generation where it's actually available, meaning that even those people who did have one didn't get to put much use into it. It's a shame, as Ash-Greninja is a very cool idea, and the Bond Phenomenon in general should've been better used, both in the games and in the later iterations of the anime. Alas, Ash-Greninja was too good for this Pokémon world.