I looked for Pokémon on the challenges database and all I can see is Pokémon Red, Blue and Yellow. None of the others. Please add the rest.

I actually brought it up a couple days ago in the challenge ideas thread. I personally would like to see something like this:

(Copied from other thread)
Gen 1: (Red, Blue, or Green) + Yellow
Gen 2: (Gold or Silver) + Crystal
Gen 3: (Ruby or Sapphire) + Emerald + (FireRed or LeafGreen)
Gen 4: (Diamond or Pearl) + Platinum + (HeartGold or SoulSilver)
Gen 5: (Black or White) + (Black 2 or White 2)
Gen 6: (X or Y) + (Omega Ruby or Alpha Sapphire)
Gen 7: (Sun or Moon) + (Ultra Sun or Ultra Moon) + (Let's Go Pikachu or Let's Go Eevee)
Gen 8: (Sword or Shield) + Isle of Armor + Crown Tundra + (Brilliant Diamond or Shining Pearl) + Legends Arceus

An argument can be made for including third/expansion games as part of the first set of two (this would include Crystal, Emerald, Platinum, and Ultra Sun/Moon), but I feel like there's a large enough difference in content to warrant the separation. Could also be separated by platform. (GB/GBC, GBA, DS, 3DS, NS)