"It destroyed its own control mask. It has become capable of changing its type by equipping special memories. Upon awakening, its RKS System is activated. By employing specific memories, this Pokémon can adapt its type to confound its enemies."
Type: Null was created by Faba of the Aether Foundation to be an "Anti-UB Fighting life-form". Codenamed "Beast Killer", Type: Null was developed with cells taken from all known Pokémon types. This was done with the intention of giving it the ability to shift between types by holding a corresponding memory, an ability originally inspired by the myths researched at Canalave Library. This ability led the Aether Foundation to give it the name Type: Full. Three known models of Type: Full were created, but all three rejected the RKS System and went berserk. After being subdued, the three Type: Full were given limiter helmets to lessen the effects of the RKS System's rejection and were put into permanent cryogenic stasis. Thus, the Beast Killer Project was deemed a failure, and the creature's name changed to Type: Null. Two of the subjects were destroyed, while the third was put back into testing due to Giovanni's plans.
Type: Null first appeared in AE003 under the ownership of Faba, having been used during the battle with Kartana. Lexi was fascinated by it, however Faba simply disregarded it as an "experiment". Lexi saw it being used again when Faba accompanied them to try and capture Poipole, having been ordered to kill the creature before being stopped by Lexi. It was during this confrontation that Lexi saw Type: Null react; realisizing it was scared of Faba. However, due to Annabel's collapse, she was unable to do anything at that time. It is used once again by Faba at the Aether Foundation under the orders to attack Lexi, Zinnia, Annabel and Looker, which it was obeying to until it was unable to attack Lexi despite a strict command from Faba. In AE008, Lexi uncovers notes revealing the mistreatment and origin of Type: Null's creation, and then manages to find it and releases it from Faba's ownership, telling it to run and be free. However, it returned to Lexi's side to help her defeat the Ultra Beasts, for the first time trying to defeat them to be captured rather than kill them. Type: Null then remained with Lexi when she ran away to Galar.
When Lexi arrived in Galar, she kept Type: Null secret in order to protect it, unsure of what its revelation would bring. After attempting to train Yamper in Wedgehurst, Type: Null endured a seizure of PTSD which caused it to lose control and cause havoc. After attempting to stop it, and coming into contact with Calem and Marlon again, they successfully calmed it down. Lexi was cautious of using it in battles following this, however after a training session with it Lexi decided to use it duirng her Gym Battle with Milo. It's success in this battle caused Lexi to be determined to train it further, including removing its limiter helmet.
Type: Null continued to be used following this, including battles against Nessa, Kabu, Allister and Bea. Continuing to show improvement - it was only after the group were attacked by a Gigantamaxed Sandaconda causes a sandstorm which nearly killed Lexi in which Type: Null was able to remove its helmet, and evolved into Silvally. Due to this, Lexi was finally able to utilise the RKS system within it to change its types due to different memories it posessed.
Lexi considers it to be her strongest Pokémon.
Type: Null, as a Synthetic Pokémon, seemed to be emotionless when first introduced. Under the ownership of Faba, it didn't react to any situation, even battling with little expression. The first time emotion was seen was when Lexi stopped it from killing Kartana, realising it was scared of Faba hence why he obeyed every command. The next time, was when Faba demanded for it to "kill" Lexi and her friends, being unable to do so. Finally, it was unable to hide its gratitude when Lexi released it.
Following this, Lexi tried her hardest to garner emotion from it. Although it continued to show little to no emotions, Lexi discovered this was trained into it, rather than its personality, due to its past and upbringing from creation. As time progressed, Type: Null showed more and more emotion, becoming more passionate about battling and caring towards Lexi and her other Pokémon. Due to this, it later evolved into Sivally, where its loyalty transformed into strength due to it and Lexi's bond.
Silvally has the ability to change types when it is holding onto any type of memory. His speed is greatly increased.