There is a special kind of riff that makes you check whether your amp is broken, your strings are dead, or the universe simply hates you. The intro to Opeth's "Deliverance" is all three at once, on purpose, and it is fantastic. Half a minute of low, groaning dread that somehow grooves.
This little clip breaks down that tritone-driven intro riff. It is the dark, dissonant prog-metal figure that anchors the whole song, and the good news for your fingers is that it sounds ten times harder than it is to actually play.
How this tritone riff works
The whole thing is built around the tritone, the interval theory nerds call the devil's interval. It sits six semitones apart, splits the octave exactly in half, and is the most restless, unresolved sound in Western music. Opeth just leans on it, refuses to resolve it, and lets it stew. Here is the properly nerdy bit: the tritone is its own complementary interval, so flip it upside down and you get another tritone, which is why it always sounds equally uneasy no matter which note you sit on.
Practically: tune down a whole step for that cavernous low tone, keep your palm firmly on the bridge so every note is choked and heavy, and let the space between notes do the scaring. The takeaway is that dread is a rhythm technique as much as a pitch one. If your palm mutes are mushy, none of the menace lands, so drill those first.
Nail it and your neighbours will assume you summoned something. Want the full PDF and Guitar Pro file so you can summon it accurately, one Opeth riff at a time? It's all waiting on my Patreon.