It shouldn't matter what the original song genre(s) were, just as long as it was done in a metal music style for the cover.
Caleb Canatheviphth's ‘Hammer Smashed Face’
Eddy Jaber's ‘True black metal Bach choral : O haupt voll blut und wunden (BWV244)’
Zachary J.'s ‘Night on Bald Mountain’ (not AI, despite the image)
Therion did an entire album and an EP of covers of 60s' French pop songs: e.g. ‘Nous ne sommes pas des anges’ and ‘L'amour est bleu (mellow version)’ or the heavy version. They also have gorgeous cover of ‘Summer Night City’.
Le Scrawl's ‘Ring, Ring, Ring’
Sasha Garcia's ‘The Cereal Mouse’, if this counts; and also his ‘Mutilate the Stillborn’