Fireflies, a mob that only consists of two pixels, were announced to be added in the Wild Update. Besides looking nice in the new mangrove swamp biome, the primary use for fireflies was to be eaten by frogs. Mojang then found out that eating fireflies is harmful to frogs in real life, and they didn't want to encourage players to go on a frog poisoning rampage. As of now it is unclear whether fireflies will still be added to the game or not. By downloading this add-on, however, you can still use fireflies in your game! While they cannot be eaten by frogs, they can still add ambiance to your worlds.