Choice Specs are one of the items that can be held by Pokémon. They can be found as a drop from any Boss Pokémon.
Choice Specs raise the special attack stat of the Pokémon holding them by 1.5x, but restrict the holder to using one move until it is recalled.
As of version 2.2.1 of Pixelmon, the Choice Band, Choice Scarf, and Choice Specs will apply their respective buffs to the Pokémon using them, but they don't force the Pokémon to only use the first move it used in battle. This bug makes these items overpowered.