Fist Plate
From Pixelmon Wiki
A Fist Plate is a held item that raises the power of the holder's Fighting-type moves by 20%. When held by Arceus, its typing and its signature move Judgment become Fighting-type, and it and any Fighting-type move receive the power boost.
It can be obtained as a drop from legendary boss Pokémon, from Beast Chests, and from chests found in Strongholds.