Did you know that there's a Poison-type Eeveelution?
It's called Burakkī. It's actually from Gen 2, the Gold/Silver Spaceworld '97 demo, which is in Japanese. It evolves from Eevee with something called a Poison Stone. Obviously it didn't make the final cut, same with quite a few Pokemon from the Spaceworld demo. There was also Rīfi, a Grass-type Eeveelution that evolved from Eevee with the Leaf Stone. While it didn't make it to Gen 2, Leafeon was introduced in Gen 4, so they kept the idea at least. They also had Ēfi, a Psychic-type Eeveelution that evolved with a 'Heart Stone'. It seems to be Espeon, so they kept that. Sadly I can't compare them by pictures since Bulbapedia didn't show me one of Ēfi. Funnily enough, there seemed to be no Umbreon at all. Sad.
They scrapped more than just a couple Eeveelutions. For example, there was Mikon, a Water-type pre-evolution of Vulpix, and Shibirefugu, an evolved form of what seemed to be Qwilfish. There were also Pokemon like Manbō1, a Water-type Pokemon, and its evolutions, Ikari and Gurotesu, which were both Water/Steel-type.
Very fascinating.
https://bulbapedia.bulbagarden.net/wiki/Pok%C3%A9mon_Gold_and_Silver_Spaceworld_%2797_demo
https://bulbapedia.bulbagarden.net/wiki/Pok%C3%A9mon_Gold_and_Silver_Spaceworld_%2797_demo/Pok%C3%A9mon