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

Six Feet Under DOOMSDAY
Tuning DGCFAD
* palm mute

INTRO
D---------------------------------------------------------|
A---------------------------------------------------------|
F---------------------------------------------------------| x4
C--5-----6--7---------------5-----7--6--------------------|
G--3--5--4--5---------------3--5--5--4--------------------|
D-----3--------666666666666----3--------555555555555------|
               ************             ************

RIFF A
D------------------------------|
A------------------------------|
F------------------------------| x 2
C--3-------4------3------------|
G--1---3---2------1---3---2----|
D------1--------------1---0----|

Intro x4
Riff A x2
Intro x2, then...

Riff B
D--------------------------------------|
A--------------------------------------|
F--------------------------------------| X 2
C--------------------------------------|
G--------------------------------------|
D--55555555-33333333-11111111-00000000-|
   ******** ******** ******** ********
  then....
Riff C
D--------------------|
A--------------------|
F--------------------|repeat x 8
C--------------------|
G--2--3--5--3--2--3--|
D--0--1--3--1--0--1--|
   *  *  *  *  *  *
Riff A x 2
Riff C x 8
Riff A x 2 (Doomsday!! part)
Riff C x 8

Intro x 4

then.....

D-------------------------------------|
A-------------------------------------|
F-------------------------------------| x 1
C-------------------------------------|
G-------------------------------------|
D-55555555-33333333-11111111-00000000-|
  ******** ******** ******** ********

Riff C x 4
then..
D------|
A------|
F------|
C------|
G---2--| end
D---0--|