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 gain animal attributes, 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. All SMILE users seen so far can be identified by either having two horns on top of their head or having their ears transformed into those of the animal's.
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. 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. Others seem to have animals growing out of the top of their heads making the animals resemble hats or hair, as seen with fox and walrus SMILE users.
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.
List of SMILE Types
Ram - Allows the user to transform their hands into sheep horns. Eaten by Sheepshead.
Crab - Allows the user to have a crab claw. Eaten by a gifter present at Zou.
Mouse (ネズミ,Nezumi?) - Allows the user to gain mouse ears. Eaten by Mouseman, and by another gifter present at Zou.
Stag beetle - Eaten by a gifter present at Zou.
Sea urchin - Eaten by a gifter present at Zou.
Bat (コウモリ,Kōmori?) - Allows the user to gain large bat wings on his waist and bat ears that give them good hearing abilities. Eaten by Batman. Also, a member of the non-canon Grip Trio, ate a SMILE that turn the user's arm into a bat. Another gifter present at Zou ate this SMILE.
Gazelle (ガゼル,Gazeru?) - Allows the user to transform their legs into a gazelle's legs that grant that enable them to run 200 kilometers an hour. Eaten by Gazelleman.
Lion (ライオン,Raion?) - Allows the user to generate a lion's head and forelegs on their waist. The side-effect is that the lion's head has a mind of it's own. Eaten by Holdem.
Horse (ウマ,Uma?) - Allows the user to gain the ears and lower body of a horse giving them a centaur-like appearance while also enhancing their vision and speed. Eaten by Speed.
Hippopotamus (カバ,Kaba?) - Allows the user's body to grow a hippopotamus body from the back of their legs. The side effect is that the hippopotamus body has a mind of it's own. Eaten by Dobon
Snake - Allows the user's arm to become a snake. Eaten by a gifter present at Zou, and by a member of the Grip Trio.
Alpaca (アルパカ,Arupaka?) - Allows the user to have an alpaca neck, ears and lips. Eaten by Alpacaman.
Scorpion - Allows the user to have six legs and a scorpion stinger in his hair. Eaten by Daifugo. Also a member of the non-canon Grip Trio ate a SMILE that allows the user's arm to become a scorpion claw.
Elephant - Allows the user to have a elephant head in the belly. Eaten by Babanuki.
‡: the character is no longer part of this group. Hovering the symbol may give further details.
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.
Doflamingo first mentioned SMILEs to Disco just before he abandoned the slave trade.
The Gifters' ability to turn selective parts of their body into animals (and animals parts) is similar to Marco's control of his Devil Fruit.
Some SMILE Devil Fruit users possess a fruit that has the ability of another, already existing Devil Fruit.