Universal Pokemon Editor
Works on most games and systems, including:
Gen 1 (GameBoy): Pokemon Red, Blue, and Yellow (and possibly Green).
Gen 2 (GameBoy Color): Pokemon Silver, Gold, and Crystal.
Gen 3 (GameBoy Advance): Pokemon Emerald, Ruby, Sapphire, Fire Red, and LeafGreen.
Gen 4 (NDS): Pokemon Diamond, Pearl, Platinum, HeartGold, and SoulSilver.
Gen 5 (NDS): Pokemon Black, White, Black 2, and White 2.
Gen 6 (3DS): Pokemon X, Y, Omega Ruby, and Alpha Sapphire.
Gen 7 (3DS): Pokemon Sun, Moon, Ultra Sun, and Ultra Moon.
Will probably work on the Japanese versions as well, but haven't tested those yet.
There are a total of 802 Pokemon you can edit (if you're editing a 7th generation game).
Download Universal Pokemon Editor version 0.9
Editor will auto-detect which generation you have, so all you have to do is open your ROM and the editor is ready to edit.