I am 99% this is correct.  Tabbed it by ear.
Here it is, KEEP IT METAL!!!!

Six Feet Under DOOMSDAY
Tuning CFA#D#GC
* palm mute

INTRO
----------------------------------------------------------|
----------------------------------------------------------|
----------------------------------------------------------| x4
--7-----8--9----------------7-----9--8--------------------|
--5--7--6--7----------------5--7--7--6--------------------|
-----5---------888888888888----5--------777777777777------|
               ************             ************

RIFF A
----------------------------------------------------------|
----------------------------------------------------------|
----------------------------------------------------------|
--5-------6------5-------5------5-------6------5----------|
--3---5---4------3---5---3------3---5---4------3---5---4--|
------3--------------3--------------3--------------3---2--|

Intro x4
Riff A
Intro x2, then...

Riff B
-----------------------------------|
-----------------------------------|
-----------------------------------| X 2
-----------------------------------|
-----------------------------------|
--77777777555555553333333311111111-|
  ********************************

  then....
Riff C
--------------------|
--------------------|
--------------------|repeat x 8
--------------------|
--2--5--6--5--2--3--|
--0--3--4--3--0--1--|
  *  *  *  *  *  *
Riff A
Riff C x 8
Riff A (Doomsday!! part)
Riff C x 8

Intro x 4

then.....

-----------------------------------|
-----------------------------------|
-----------------------------------| x 1
-----------------------------------|
-----------------------------------|
--77777777555555553333333311111111-|
  ********************************

Riff C x 4
then..
------|
------|
------|
------|
---2--| end
---0--|