Throughout the entire game, you are given Z-crystals upon completion of your island challenges. When your Pokemon is given a Z-crystal to hold, they’re essentially given a 5th move to their move sets. Your Pokemon can only use a Z-crystal if it has a move of that type in its move set. For example: a Firium Z can be held if the Pokemon knows a Fire-type attack.

There are also 2 ways Z-crystals transform regular moves. There are damage-dealing and non-damage-dealing Z moves–just like normal moves. The power of the Z move also depends on the move that is being turned on by the Z-crystal. The more powerful the base move is, the more powerful the Z move is. Non-damage-dealing Z moves will boost, reset, or restore stats or HP of your Pokemon. A couple moves can also make moves target the user, so bewear (hehe, it’s punny).

Some Z-crystals are Pokemon specific as well as move specific. A Decidium Z can only be held/used by Decidueye. In order to use the Z move Catastropika, Pikachu must be holding a Pikanium Z and know the move Volt Tackle.

With that said, here is the list of Z-crystals and where to find them. Note that there are a few given to you through trade from NPCs in the game, those however are not going to be marked here. These are the main ways to obtain the crystals.

Aloraichium Z Stoked Sparksurfer Receive in from a woman in Seafolk Village
Buginium Z Savage Spin-Out Pick it up after battling Guzma in the Shady House
Darkinium Z Black Hole Eclipse Clear Ula’ula Island’s Grand Trial
Decidium Z Sinister Arrow Raid Receive from Kukui in Malie Garden if you chose Rowlet, or receive from Hau after becoming Champion
Dragonium Z Devastating Drake Clear the abandoned trial on Poni Island
Eevium Z Extreme Evoboost Complete the “Eevee Trainers” sub-event after becoming Champion
Electrium Z Gigavolt Havoc Clear Sophocles’ island trial
Fairium Z Twinkle Tackle Receive from Mina on Poni Island
Fightinium Z All-Out Pummeling Clear Melemele Island’s grand trial
Firium Z Inferno Overdrive Clear Kiawe’s island trial
Flyinium Z Supersonic Skystrike Find it in Ten Caret Hill
Ghostium Z Never0Ending Nightmare Clear Acerola’s island trial
Grassium Z Bloom Doom Clear Mallow’s island trial
Groundium Z Tectonic Rage Clear Poni Island’s Grand Trial
Icium Z Subzero Slammer Find it on Mount Lanakila
Incinium Z Malicious Moonsault Receive it from Kukui in Malie Garden if you chose Litten, or receive from Hau after becoming Champion
Normalium Z Breakneck Blitz Clear Ilima’s island trial
Pikanium Z Catastropika Receive from woman in Konikoni City
Poisonium Z Acid Downpour Receive after battling Plumeria on Poni Island
Primarium Z Oceanic Operetta Receive if from Kukui in Malie Garden if you chose Popplio, or receive from Hau after becoming Champion
Psychium Z Shattered Psyche Find it in the Haina Desert
Rockium Z Continental Crush Clear Akala Island’s grand trial
Steelium Z Corkscrew Crash Receive from Molayne after clearing Sophocles’ island trial
Tapunium Z Guardian of Alola Pick it up after becoming Champion and battling Tapu Koko on Melemele Island
Waterium Z Hydro Vortex Clear Lana’s island trial