The tentacles that we see trying to escape from The Plague's basement are Cthulhu's tentacles, and since he lives near the town where the movie takes place, he drove all the residents there insane. This would explain Hope Town's ludicrous, Up to Eleven amounts of depravity.
Those who supported his vigilantism but didn't want to incur Drake's wrath by openly helping him would buy shotgun shells and leave them out in public places for him to find, which is why he never ran out.
Nick Bateman voices both Rip and Ivan...
Abby and the decent people of Hope Town finally got fed up with Drake and the corrupt police force and began fighting back. The Hobo story was only a story passed around to create a heroic figure for the people to rally behind as they took back their town.
The hobo was a judge from the early years (during the timeline of Origins) but before the bombs nuked America and Canada into the Cursed Earth. The hobo left for unspecified reasons (perhaps mental illness, which is why he can't remember) and was one of the earliest judges to take the long walk option. Order was breaking down across America, resulting in the city we see the hobo wander into. He wasn't sure about taking law to the lawless until he has to choose between the lawnmower and the shotgun, when his training and experience kicks in.
- "Order was breaking down across America, resulting in the city we see the hobo wander into." - I hope you meant 'North America'/'the Americas', not just 'America' as in the USA, because the movie was filmed in, created by two guys from (and written by one and directed by the other), and 'vaguely' set in, Canada.
- To be fair, it's left ambiguous whether or not Hobo With a Shotgun is set in America or Canada. That being said, it could be in either of those countries, as none of the logos shown in the movie scenes indicate which country it is and Canadian terms such as "Constable", "Toque", or any other Canadian terms are not used in the movie.