Tis_Bearself:
It’s also known as a “death growl”. It’s a vocal technique used in a lot of death metal, black metal, and some hardcore.
AKA “Cookie Monster vocals” to some of us slightly older metal fans.
It was really unusual and unique back in the early 90s/late 80s, but by now its been overused. Cookie monster growlers are a dime a dozen and infinitely replaceable because most anybody can do it.
Sounding evil and demonic is the entire point of it.