Suicidal black metal is intriguing. I find few characteristics in common between the suicidal bands that I've heard. Outside of lyrics, and more extreme than usual vocals, I do not know what defines suicidal BM bands. Silencer is often said to be one of the legendary bands of the genre, but my initial impression was that outside of the lyrics and vocals, the music did not substantially differ from other black metal. The vocals lacked the heavy effects and distortion that I was used to hearing in suicidal bands, and the production was surprisingly clean.
Leviathan also has many melodic riffs and rock style drum beats that induce fits of headbanging, not wrist-slashing. I love the music, but am somewhat confused by the classification.