If held by a Houndoom, the Houndoominite allows it to Mega Evolve into Mega Houndoom if its Trainer has a Key Stone. A Trainer can only Mega Evolve one Pokémon per battle (or only have one Mega-Evolved Pokémon at any given momentZA).
As a Mega Stone, it is unaffected by item-negating effects (such as Embargo and Klutz). Item-manipulating effects (such as Trick and Fling) cannot give or remove a Houndoominite from Houndoom.
Outside of battle
If held by a Houndoom, the Houndoominite allows it to Mega Evolve into Mega Houndoom when it performs a Spectacular Talent during a Pokémon Contest Spectacular if its Trainer has a Key Stone. Houndoom will remain a Mega Houndoom until the Talent Round ends.
The player can obtain the Houndoominite by completing the competitive stage available in Week 19 of the event rotation.
The Houndoominite was also available as a prize during the Mega Houndoom competitive stage. This competitive stage ran on both the Nintendo 3DS and Mobile versions from January 17 to 24, 2017; and April 11 to 18, 2017.
The Houndoominite enables the following Mega Evolution:
Mega Ring System Houndoominite
Houndoom, Mega Houndoom & Houndoominite metal charm set
