Don't quote me on this, but it's pretty much Emerald with the ability to get all Pokes from Gen II and I, rather than just the normal 3rd gen stuff.
What I know of it is that it's more difficult than the regular Emerald. Any specific eeveelution you want? By team I prob would have to go Jolteon or Espeon, though I've never tried the Espeon/Umbreon evolving method so I can't guarantee I'd get one or the other. (If I use Eevee at all, or get it at all)
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My sig needs changing. I'll get a better one later.