Unaffected by item negating effects (such as Embargo and Klutz). Item manipulating effects (such as Trick and Fling) cannot remove a Z-Crystal from a Pokémon.
An Eevium Z first appeared in Turning Heads and Training Hard!, where Kagetora gave it to Ilima after being defeated by him in a battle. Later in the episode, Ilima used the Z-Crystal with his Eevee to perform Extreme Evoboost while fighting a group of Team Skull Grunts. As a result, Eevee was given a massive power boost that allowed it to easily defeat the Grunts and send them blasting off.
Another Eevium Z appeared in SM114, where it was stolen from Kagetora by a Pheromosa.