In the core series games
If held by a Slowbro (or is present in the player's Bag)PE, allows it to Mega Evolve into Mega Slowbro if its Trainer has a Key Stone. Each Trainer can only Mega Evolve one Pokémon per battle.
Unaffected by item negating effects (such as Embargo and Klutz). Item manipulating effects (such as Trick and Fling) cannot give Slowbro a Slowbronite or remove a Slowbronite from Slowbro.
Outside of battle
If held by a Slowbro, allows it to Mega Evolve into Mega Slowbro when it performs a Spectacular Talent during a Pokémon Contest Spectacular while its Trainer has a Key Stone. Slowbro will remain a Mega Slowbro until the Talent Round ends.
Pokémon holding Slowbronite in Pokémon Omega Ruby and Alpha Sapphire cannot be traded to Pokémon X and Y.
| One of a variety of mysterious Mega Stones. Have Slowbro hold it, and this stone will enable it to Mega Evolve during battle.
|| One of a variety of mysterious Mega Stones. This stone will enable Slowbro to Mega Evolve during battle.
In the manga
In the Pokémon Adventures manga
In Omega Alpha Adventure 7, Jinga was revealed to possess a Slowbronite, which he used to Mega Evolve his Slowbro.
In other languages
|| 呆殼獸進化石 Dāikéshòu Jìnhuà Shí
|| 呆殼獸進化石 / 呆壳兽进化石 Ngòihhoksau Jeunfa Sehk
|| 야도란나이트 Yadonrannite