Throughout 2014 and into 2015, synthwave as a genre has been bleeding into the metal scene by way of artists like Gost, Dan Terminus and Perturbator and labels like Blood Music. It's not a bad thing! At the heart of both sounds there are some similarities, such as pounding drums, relentless riffs and even some shreddy bits here and there. Obviously "similar" is a loosely-used term here but you get the picture.
So in my synth-seeking adventures, I came across an appropriate vendor of the genre called titled Werkstatt Recordings. That label had released a compilation titled Altars of Synthness, which is classic metal songs by bands like Slayer and Bathory covered in the style of synthwave by artists like Fixions, Mach Rider, The Deathless and a whole lot more! You seriously need to check some of these out.
My favorites are "Dirge For November" by Opeth, as interpreted by Vincenzo Salvia and "You Suffer" by Napalm Death, interpreted insanely by Hydraulic Anus. Check it out!