The player can obtain the Latiosite by passing Level 50 on a Mega Latias Escalation Battle in Weeks 4 and 5 of the event rotation.
The Latiosite was also available as a prize during the Mega Latios Escalation Battles prior to the event rotation system. This Escalation Battle ran on the Nintendo 3DS version from November 24 to December 8, 2015; April 26 to May 10, 2016; June 27 to July 11, 2017; and January 9 to 23, 2018. It ran on the Pokémon Shuffle Mobile from April 26 to May 10, 2016; June 27 to July 11, 2017; and January 9 to 23, 2018.
The Latiosite enables the following Mega Evolution:
Data for Latiosite exists within the code of Pokémon X and Y, despite the Mega Stone not being officially introduced until Omega Ruby and Alpha Sapphire, allowing it to be transferred to and used in X and Y. It shares this trait with the Latiasite.