Wow.
Ok so i wanted to say that "most metal covers are just the same song with a distortion pedal and double kick".
Now, Leo is the epitomy of the non-metal metal cover, and considering how much people here like him, im not sure how well this'post gon'go down.
The thing is, metal is based on different intervals, so unless you already got a shitton of minor chords in there, no amount of metallizing-beam can turn a non-metal song into metal.
It does work great the other way around tho.
Well, most of the time.
See Rob Scallion, or Steve & Seagulls, or 2Cellos. And Brown Sabbath.
And you should also check out Beatallica because Beatallica makes everything better.
Oh and ... Children Of Bodom did a whole album of covers, "Skeletons In The Closet".