Riff A
G--------------------------------|
D--------------------------------|
A--------------------------------|
E-7-7h8--7-7h8--7-7h8--3--5555---|
Riff B
G-----------------------------------|
D-----------------------------------|
A-----------------------------------|
E-7-7---1-1---5-5-5h6p5h6h5p6h5h6---|
Riff C
[ Tab from: https://www.guitartabs.cc/tabs/p/pentagram/the_ghoul_btab.html ]
G---------------------------------------------------------------|
D---------------------------------------------------------------|
A--------7h9h1097--------7h9h1097---------3h5h653-------3h5h653-|
E-7-7-7-----------7-7-7-------------3-3-3---------3-3-3---------|
Those three riffs comprise pretty much the whole song, maybe with a bass fill or two.
listen to the song to figure out where to place them.