This has been going on for years now, the genre is known as Mashup'.
I admit i've become quite fond of several of these bastardizations, plainly a lot of skill required in putting them together & often the results are pretty humourous. Loads of good Metallic examples out there, some of the best being on the free DJ SCHMOLLI Mash-Up EP called 'Slayed, Chopped And Recycled : A Bastard Pop Tribute To Slayer' which you can d/l here: https://djschmolli.com/slayed-chopped-and-recycled-ep/
Also well worth checking out are examples by DJ CUMMERBUND & the excellent WAX AUDIO.
You can enjoy it for what it is or get bent out of shape about it, but it's not meant to be taken too seriously. One man's sacrilege is merely another's humorous diversion. I've still got my fingers crossed that someone may someday see fit to cross-pollinate Cirith Ungol with Funkadelic, i can imagine that combo working well together for some reason.
I cannot, I shall not, I will not obey. Avenger wrote : I'm not a copyright office nor a judicial entity.