Considering Pikachu's immense rise to popularity in the original Pokémon games and anime, it was almost a sure bet that the "baby" version of Pikachu, Pichu, would be a hit when it was released within Gold and Silver back in 1999. You might be surprised to find out that Pichu wasn't always the same little yellow creature though, and its original design was a bit stranger than the one we're used to today.
In the 1997 beta version of Pokémon Gold and Silver, Pichu had a face that more closely resembled Pikachu, but as a tiny little ball. The original version also gave Pichu completely black ears and feet. Not only that, but Pichu was originally supposed to evolve in Pikachu by reaching level 12, but Game Freak decided to change its evolution to being based on happiness upon launch.
Game Freak decided to stick with the all black tail on Pichu, but instead reworked its shape to more closely resemble Pikachu's tail. They also gave Pichu a neck, made it a bit thinner, and made only the tips of its ears black instead of the entire ears all together. Although the beta version might more closely resemble Pikachu, it's hard to choose this version over the Pichu that made it to launch.
Pichu wasn't the only Generation 2 Pokémon to get a reworked design in between Gold and Silver's beta launch and official release date. A demo leak back in 2018 revealed that the original designs for many Pokémon had been a bit different from the final product, including a two-headed Girafarig, an Ariados that looked exactly like a spider, and original Pokémon that were dropped entirely.
Still, this leaked version of the original Pichu makes us wonder what would have happened if many of these designs hadn't been altered. A good handful of the Pokémon we know today would look completely different, and others would be completely new. One can only speculate as to how this would have effected the series in the long run.
If you're looking for new Pokémon that are in fact canon, you can find an entirely new generation within Pokémon Sword and Shield, with more being introduced in the game's upcoming DLC, The Isle of Armor and The Crown Tundra. Who knows what some of these original Pokémon sprites would look like in Sword and Shield if they would have made it to see Gold and Silver's release date.
Source: Twitter/DrLavaYT