Before the re-release of Florr.io, there was a secret mob with the Unique rarity (pink), the Square. It drops a Square petal, which has the same Unique rarity and is completely useless. In the re-release, Unique was replaced by Mythic (cyan), and because of the changes every mob has a Mythic variant. According to the changelog, there are also Mythic petals, but Mythic mobs do not drop them and they can only be obtained by crafting with Legendary (red) petals. The existence of Mythic mobs is proven by the 6th column in the Mob Gallery (which was added 2 or 3 updates ago).
