Fluffy ponies, more commonly referred to simply as fluffies, are genetically engineered "biotoys" created by Hasbro under the name "Hasbio" to be sold as My Little Pony merchandise. They are naturally happy, playful creatures who enjoy giving hugs and often get themselves killed through blind trust in humans. Most headcanons accept that they are "unfinished products", prematurely unveiled to the public when a terrorist attack by a PETA splinter group released prototype fluffies into the wild.
The fluffy pony design varies depending on the artist, but they are generally small, vaguely horse-like creatures, although some are a bit larger, particularly "earthie" fluffies. Some artists and writers depict them with stubby legs that don't bend at all, while others give them legs that more closely resemble those of a real animal. Fluffy hooves are soft and leathery instead of being made of keratin, although feral life can cause them to develop hard calluses. They possess manes and tails, both typically the same color, as well as a short snout. Pegasus fluffies have small wings, unicorns have a single horn on their forehead, and alicorns have both wings and a horn, while earthies have neither. As their name would imply, they are covered in fluffy fur, which can come in practically any color imaginable, as can their eyes and mane. This includes so-called "poopy" colors, such as brown and certain shades of green.
Fluffies are usually sweet, loving creatures who enjoy playing with toys, giving hugs, and generally having fun. They have the intelligence and demeanor of a very young human child, and are capable of speech. Almost all fluffies hate water in a similar manner to cats and show a particular fondness for spaghetti, happily gobbling it down at any chance they get, although their definition of what qualifies as spaghetti varies from artist to artist. Some artists' fluffies know what actual spaghetti looks and tastes like, but others may believe any old noodles to be spaghetti and be satisfied with that.
Fluffies are not very intelligent, and thanks to this, combined with the fact that a normal fluffy tends to take anything a human says to be fact, it is incredibly easy to trick them into things such as believing instant ramen with ketchup in it to be the coveted "sketties", eating their own young in the belief that they will go back into the mother's womb and continue development, or even willingly walking to their own deaths. They have a strong desire to raise offspring, although in fluffies with Smarty Syndrome, this can simply be lust, craving the act of mating ("special huggies") itself.
The different types of fluffy also have different characteristics. Earthies are a bit more dim-witted than average, pegasi are adventurous and love flying, unicorns are dominant and more likely to develop Smarty Syndrome, and alicorns are particularly intelligent among fluffies.
The fluffy pony genome is an incoherent mishmash of genetics from other animals, notably human DNA for the speech. Their digestive systems are very inefficient, with food rocketing through the body and only having half its nutrients absorbed. This means that fluffies need to eat more than other animals, and they also defecate more frequently and in larger quantities. The body of a fluffy pony is commonly depicted as being very fragile, sometimes to an unrealistic degree, such as fluffies breaking their legs from six-inch drops. They are mentally weak as well, with particularly unintelligent interpretations capable of suffocating to death by thinking about water for too long and forgetting to breathe.
Fluffies breed and grow very quickly, surviving in the wild through sheer numbers after the initial raid on Hasbio by PETA. A number of headcanons have the government classifying them as vermin, as they destroy crops and leave trails of waste and corpses wherever they go.