Pokemon will breed if they are from opposite genders and have a matching Egg group, or if one of the partners is Ditto. They will not breed if they are the same gender as each other, if they do not have a matching Egg group, if a Pokemon is from the Undiscovered Egg group or if one of the Pokemon is genderless. (Note that genderless Pokemon can breed with Ditto, which is an exception to just about every breeding rule in the game.) Based on this, your Umbreon will breed with any Pokemon from the opposite gender that also belongs to the Field Egg group (or is Ditto).
However, in Generation II only, if the two Pokemon's IVs are too similar, they will not breed with each other. This is an extremely rare occurrence all things considered, and unfortunately, the two Pokemon you're breeding for a Shiny Eevee fall under this category. According to that same Bulbapedia page you were reading, if both Pokemon's Defence IVs are the same and their Special IVs are different by 0 or 8, the "It's brimming with energy" message will appear. As you know, that means that the Pokemon have a 0% chance of breeding. Unfortunately, as IVs cannot be changed, you will have to change Umbreon's breeding partner in order to get an Egg.
Changing Umbreon's breeding partner should be simple enough. However, unfortunately this is not the only issue standing in your way. Shininess is not one of the things that a baby Pokemon can inherit from its parents. In other words, the fact that you're breeding with a Shiny Umbreon doesn't mean the resulting baby Eevee will be Shiny. However, you're lucky that you're playing a Generation II game. IVs play a role in determining whether a Pokemon is Shiny in Generation II, and since babies inherit IVs from their parents, the baby Eevee could have as high as a 1/64 chance of being Shiny. That might not sound like much, but when you compare that to the dreadful 1/4096 in more recent games, you're in luck.
So, to sum this up for you if it didn't make any sense:
- Due to complications with IVs in the game you're playing, Umbreon and its breeding partner aren't compatible. To fix this, change Umbreon's breeding partner to a Pokemon of the opposite gender that is from the Field Egg group. This will only occur in Generation II games like Crystal.
- Because you're breeding with a Shiny Pokemon doesn't mean that its offspring will always be Shiny. However, due more complicated mechanics with IVs in Generation II, the baby has as high as a 1/64 chance of being Shiny. Compared to 1/4096 in X /Y and OR/AS, your chances are pretty good. You'll just need some patience with your breeding.
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