Zygarde Quest

The Zygarde Quest was released on March 12th 2018 as a new feature and includes all five formes of Zygarde.
In order to unlock this quest, you need to spend at least 500 gems of any type on regular gem trades with the collector.

Hatching any Zygarde egg will count towards your Shiny Chain!
You can shiny hunt them like any other regular shiny.

The Quest

After you unlocked the Zygarde Quest by trading any 500 gems with the collector, you will be able to merge the first set of gems to get a Zygarde Core egg. After merging those gems three-times, you unlock the next forme of Zygarde. For each forme you will need a larger gem variation. To get the full list of gems for each Zygarde forme, have a look at the spoiler below:

Egg Image	Forme	Gems
	Core	x10 x10
	Cell	x10 x10 x10 x10
	Zygarde 10%	x10 x10 x10 x10 x10 x10 x10
	Zygarde 50%	x10 x10 x10 x10 x10 x10 x10 x10 x10 x10 x10
	Zygarde 100%	x10 x10 x10 x10 x10 x10 x10 x10 x10 x10 x10 x10 x10 x10 x10 x10

Grass and Water gems are the only gems not used in the merging process.