Bloom of Frogs, by Michal Nagypal, is a Curio card later turned into the Alpha card Plague of Frogs. Many development changes are seen here, similar to other cards such as Grim Tangle.
In the title box, we find new casting cost symbols that are dramatically different from the current design of Sorcery: Contested Realm cards. Compare the Bloom of Frogs Curio Card next to its Alpha Plague of Frogs version:
Moving along to the type line text (above the gameplay mechanic text), we once again find the "Legendary" term, and further evidence to suggest that "Legendary" was the prior term for the highest level rarity that we now know as "Unique".
Regarding the game mechanic, I do not generally consider game mechanic changes to necessarily be indicative of a "Curio concept". A large majority of cards have had changes to gameplay mechanics through the years of development leading to Alpha Kickstarter fulfillment, and even in the timeframe between the Kickstarter campaign and fulfillment. We saw many of these differences in Sample Cards. However, there is one interesting finding to note in the Curio card mechanic. The mechanic indicates a difference between "attack" and "defense"....
The frogs have 0 attack and 1 defense.
When the official Sorcery Discord was established in Fall 2021 there was very active discussion between the game creators, developers, and fans about design elements. One point that was highly contested was how to treat attack and defense. Ultimately the company decided to unify attack and defense to be a single number, in an effort to simplify the gameplay.
Finally, we make our way down to the bottom of the card and for the first time discover some very interesting findings. The card shows 3 distinct elements that did not make it to the final design format for Alpha: Year, Set Card # / Set Size, and Set Symbol.
The year tells us that the design dates back to 2019; THREE years before the Kickstarter campaign and FOUR years before Alpha Kickstarter fulfillment. Also the set number is very interesting. This is another hotly contested topic, especially among collectors, who contemplate the best way to organize and display their set collections, and even what one would include in a "complete set" (Curios? Foils? Promos?). Even the set size is debated and technically unknown, since at the time of this writing the company has not disclosed what the Curios are and how many variants exist in the Alpha set. This approach would also make set numbering problematic, because it would implicitly forfeit an element of that "unknown" and "search" that they have intentionally included to re-capture the early 90s pre-mainstream internet element of card searching and discovery.