A Memory, also known as Memory Disc or Memory Drive, is an object introduced in the Pokémon Sun and Moon games in Generation VII. It is used to help Silvally and its Multi-Attack move change into any one of the 18 types through its RKS System Ability.
List of Memories
Sun and Moon
Ultra Sun and Ultra Moon
From Wicke after recieving Type: Null at Poni Wilds along after becoming champion along with every other Memory.