Power Bracer
From Pixelmon Wiki
A Power Bracer is a type of power item that can be given to a Pokémon. When a Pokémon holding a Power Bracer defeats an opponent Pokémon, it will earn the normal EV gains from the opponent along with 8 extra Attack EVs. However, the holder's Speed will be halved while wearing the Power Bracer. When a breeding Pokémon holds a Power Bracer, its Attack IV is guaranteed to be passed to its offspring.
The power bracer can be found in pillager outpost chests, or obtained as a tier 3 or 4 special drop.