At their headlining set at the Tons of Rock Festival in Oslo, Norway, Metallica welcomed Diamond Head founder Brian Tatler to the stage for their cover of “Am I Evil?,” which they last performed in 2022. Since 2023, Tatler has been a member of NWOBHM icons Saxon, who were among the 12 total bands that played on the first day of the annual festival. Obviously Metallica seized the opportunity and treated fans to a rare and special moment. Metallica have only played “Am I Evil?” 11 times since it was a regular part of the set in 2011, so the performance alone was a bit of a rarity, much less gett…