There needs to be a better way of obtaining the Ultra Rare Treasure Cards. Pigsie, Athena Battle Sight and Ninja Piglets are among the super rare drops off Loremaster. Make them cost crowns on a per card rate if needed. It defeats the purpose of having the recipe if you can't find a good source for the treasure cards. I would buy them at a cost of 50 crowns per card. I would bet there are other people that would do the same. You have some creative spells that need to be seen. The drop rate of the key bosses spells are also in the super rare category. Please consider a mega rare treasure card pack.
KI can also introduce even new plants for us gardeners (haven't had new seeds in a while [not necessarily counting the new beastman seeds since not everyone partakes in that event) that are geared towards these drops.
But, as it stands, treasure card versions for some of the more difficult spells to craft are extremely hard to come by as you stated.
While I understand that there perhaps need to be some amount of difficulty when crafting these spells; it shouldn't be within ranges of near impossible.
