Breeding combo information should be included by default in every animal description. That way there is no confusion - when the animal is available in the store, you have the info right there to know how to breed it. Every animal should have listed either "Breed X Element and X Element" or "Not Available Through Breeding" - and this information should be regularly updated whenever animals are brought back.
The fact that Storm8 does not do this implies either that their quality control is lacking or that they are intentionally withholding information from players in order to promote gem sales - or both. Either way, it reflects poorly on the company.
Also, animal rarity levels should actually mean something, and that information should be available somewhere - in the game FAQ, or SOMEWHERE. For example, "Common: Odds for breeding animal are approximately 1/x. Rare: Odds for breeding animal are approximately 1/xx." Etc. But again, by withholding this information, the game makers can manipulate the odds behind the scenes without accountability, making the chances of breeding a common much lower during the event for which it's needed, and returning them to their regular setting when the event is over - or not if they forget, because we really have no way of knowing, and it seems like they forget a lot of things.