Drop A i think?
(A E A D G B)
[ Tab from: http://www.guitaretab.com/a/anaal-nathrakh/218953.html ]
I learnt this by ear.
This is the intro riff, the really heavy one.
It's so fun to play
but thats the only riff in the song i cared to learn lol.
It repeats itself a few times, hope this helps people.
B-------------------------------|
G-------------------------------|
D-------------------------------|
A-------------------------------|
E-0-0-6-5-3-1-1/8-7-3-0-0-6-5-3-|
A-0-0-6-5-3-1-1/8-7-3-0-0-6-5-3-|