SMILEs resemble the artificial Devil Fruit that Vegapunk created; they are colorful fruits resembling apples that have spots of a different color all over them, and those spots have another spot inside each of them. Failed SMILEs lack spots on the bottom.
The key ingredient required to concoct the fruit is SAD, a substance that only Caesar Clown knows how to manufacture. As such, to produce such Devil Fruit requires Caesar's cooperation. The SAD is produced by Caesar, which then is transferred to the SMILE Factory in Dressrosa and processed into SMILE.
Due to the Tontatta Tribe'sdwarves specializing in plants, they are forced into labor in producing SMILEs, under the false belief that it is medication for their sick PrincessMansherry as incentive to increase their rate of production; and dwarves' gullibility led them to believe the lie. It appears that the Tontatta can produce only one viable fruit out of every ten SMILEs, themselves noting the unorthodox fruit complicating the success rate. The bottom quarter of the fruit lacks the telltale swirls, which seems to mark the difference between a successful fruit and a failure. The manufacturing process of the SMILE Factory involves having luminescent sunflowers that provide light to the trees growing the fruits, while SAD is poured into the river. The river has irrigation on both sides that channel the river under the trees to feed them.
With the factory and SAD supply destroyed, and Caesar in captivity, the production of SMILE has stopped.
SMILEs resemble Zoan-type Devil Fruits in that they allow the user to transform into an animal, although there are notable differences between the two. While normal Zoans can fully transform into an animal and an animal hybrid, the SMILE users seen so far have demonstrated the ability to turn certain parts of their body into non-corresponding parts of the animal's body, such as Sheepshead turning his hands into sheep's horns and other gifters turning their hands, chest, or stomach into animal heads. SMILE users can still possess various traits and abilities of their animal, such as Batman gaining sharp hearing and Gazelleman being able to run very fast.
However, when Caesar talked about Kaido's army of SMILE-users, the Gifters foreshadowed in his mind resembled full animals, indicating that they may be able to go further with their transformations.
It is unknown if SMILE users are affected by the standard Devil Fruit weaknesses of water and Seastone, but Law did mention that being artificial, they do have their potential side-effects. One such side-effect appears to be that the Gifters gain black horns on their heads. Certain Smile users also cannot undo their transformation like regular Zoan Devil Fruit users as some Gifters remained permanently transformed without being able to turn back. Another more unstable side effect is that instead of having animal features or limbs, some users will instead have an animal growing out of their body, as seen with Holdem's lion, whose head and arms are protruding from Holdem's midsection. Animals such as these will have a mind and will of their own, and this can be painful or even dangerous for the user as said animal may argue or even attack its own host. However, as the animal half shares the same body as its user, it will share any pain its host receives, which will keep the animal from attacking its host too often.
So far, very few SMILE have a confirmed animal, with the majority determined by the user's ability and transformation. The anime featured several different characters with the same animal theme like snakes and bats, and some undistinguished animals with pincers or claws, though the exact species are unknown. This is similar to some Zoan types various "models", but this is not canon.
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After the SMILEs were created in Dressrosa, they were acquired by Kaido of the Yonko, who fed them to his crewmembers in order to turn them into Gifters. Kaido's dream is to have a crew entirely consisting of Devil Fruit users, and he has amassed an army of over 500 Gifters. The Gifters use their abilities frequently during battle in order to increase their strength. However, after the SMILE Factory was destroyed, the Beasts Pirates stopped receiving SMILEs and so the production of new Gifters ceased.