Does anyone at all have a tab to "down and under"? Or at least know what key its played it? I have a terrible ear for tabbing
Main riff on the bottom C string is something like:
7-----9-----5-----4-5-4-2--4-0------
and taking some of the open strings with that as well for the different verses (obviously building intensity as the song progresses).
The little breakdown after the main riff is repeated a few times is something like:
4-5-4-2--4-0--7--7--
alternating with:
4-5-4-2--4-0--(5)-(5)-(5)-- where (5) denotes a natural harmonic. You could also play a regular 5 on the lowest G string after the first verse; as long as the note is C it doesn't really matter.

The breakdown are full chords but for simplicity's sake I will only write the bottom notes:
1--1--10------1--1--10------0--0--10------0--0--10-----
1--1--10------1--1--10------0--0--10------0--0--10-----
3--3--10------3--3--10------0--0--10------0--0--10-----
3--3--10------3--3--10------0--0--10------0--0--10-----
And then it's basically just playing all the open strings. If you like you can follow the vocal melody because it makes it more interesting to play. That would be a repeated progression on the G strings:
12--9--9--7--5--
And after that it goes back to the main riff etc. It's very simple but very fun to play, because the key is to build the song up just with your right hand (if you're a right-handed player) to get that climactic feel that it has.