Not everything is so....

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Across
  1. 2. Four-formed Pokemon based on the new overworld gimmick
  2. 3. The E4 Member who appeared a generation earlier
  3. 6. Used to be touted as the most forgettable
  4. 10. The only Pokemon to break the numbering system
  5. 11. This type combo is the only combo that would have super-effective STAB on every E4 member's primary type, without being weak to any of them as well (alphabetical)
  6. 13. Furret loves it here
  7. 15. Owner of a very frustrated Hydreigon
  8. 16. Dream World researcher
  9. 17. The only starter to gain a secondary type, to some dismay
  10. 18. This Pokemon had its hidden ability changed before it could become a menace
  11. 20. A surprising (and deserved) exclusion from the Pokedex, and its replacement
  12. 21. Three Musketeers
Down
  1. 1. The only games to not have any pre-existing Pokemon in their Pokedex (alphabetical)
  2. 4. Literal ragebaiter
  3. 5. While not being directly replaced in the gym order, the ___ type gets replaced with the ___ type in B2W2
  4. 7. First region not based on a part of Japan
  5. 8. Shared animal-based forme name of the Forces of Nature
  6. 9. This type got its first mono-type in Gen 5
  7. 11. Grandson of the objectively best Dragon-type specialist
  8. 12. The best display of Black and White's 2.5D-esque camera placement
  9. 14. In-battle microtransaction prototype
  10. 18. If you're thirsty, go talk to him in any gym
  11. 19. The gym in this town is why there are 10 gym types