Here’s that heavy main riff to The Ar by Tiamat:
Tune 1 step down (D-tuning)
Part 1 (D):
D———————|
A———————|
F———————|
C-2–2-2–2———–|
G-2–2-2–2-0-3-2—–|
D-0–0-0–0——-3-5-|
Part 2 (F):
D———————|
A———————|
F———————|
C-5–5-5–5———–|
G-5–5-5–5-3-6-5—–|
D-3–3-3–3——-6-8-|
The song starts with the end of Part 2:
D———–|
A———–|
F———–|
C———–|
G-3-6-5—–|
D——-6-8-|
The verses are really just keyboard and bass switching from D to F.