>>35822936>1. Get the shiny.>2. Make sure you have 50 cells in your Zygarde Cube.>2a. If you don't, break down a 50% Zygarde into Cells.>3. Select the option to assemble with Zygarde and Cells.This will use up the cells in your Cube and turn the shiny Zygarde's ability into Power Construct.
Of note: the game won't let you break down the shiny Zygarde into cells because of its ribbon.