I profiled a couple of cool patches for the famous Boss HM-2... with the specialty being that this is for BASS 
Probably will not sound nice with a guitar (no amp...).
You'll find them in Rig Exchange:
JU - Boss HM-2/12:00
All settings at 12:00. Kinda gritty and a bit sludgy.
JU - Boss HM-2/Messy
My favourite, really deep and heavy fuzzy explosion for Doom
JU - Boss HM-2/Sludgy
A bit more traditional grit with clearer attack
JU - Boss HM-2/Sunlight
The holy grail. Everything at MAX! Just like the classic Sunlight Studios sound this pedal is most famous for Though for bass guitar, it's not all that impressive unlike for guitar.
Have fun! 