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