I was looking at the dragons that have:
-Legend as their only element
-a Legendary Rarity
Examples: Legacy, Droconos, Tin Woodman, etc.
I noticed something.
-Timetravel, Nobunaga, Fate, and Asier can be obtained either from Collections or Offers.
-Immortal, Imp, and Sap can be obtained either in Packs or Offers.
-Dragotron, Rockfire, and Felidae can be obtained either in Quests or Offers.
-19 Dragons can be obtained from Breeding.
The only Legendary Rarity, Legend-only Dragon that is exclusive to Offers is the Impassible Dragon.
What I'm proposing: Add the Impassible Dragon as a permanent addition to the breedable dragons. That way, we'd have an even number of breedable Legends; 20 Legend-elemental dragons that are breedable.