Outsider Metal

Then you must really appreciate Alestorm who have done complete albums with dogs barking and no lyrics!!
 


dunno how much you consider Traumatic Voyage as "outsider metal" but they were pretty ahead of their time with their weirdo psychotic prog death-cum-black metal. Its very technically proficient, albeit scrambled in approach and all over the place sound wise. I remember reading Astorian having mental illness (I think schizophrenia??) and that attributed a lot to the lyrical and sound theme.

Regardless, really fucking crazy stuff.