Tadpoles are not a naturally spawning mob in Minecraft. They can only be obtained through mods or by using spawn eggs in creative mode. Therefore, the rarity of tadpoles in Minecraft depends on the availability and usage of mods or creative mode.
In some mods, tadpoles may spawn naturally in certain biomes such as swamps or be obtained through breeding frogs. However, in vanilla Minecraft, tadpoles do not exist.
In general, tadpoles are the immature form of frogs and toads, and they can be found in real-life bodies of water such as ponds, lakes, and streams. In Minecraft mods that add tadpoles, they may behave similarly to fish or other aquatic mobs, and they may have their own unique uses or interactions within the game.