This episode...well, we're kind of cheating.
It's based very, very strongly on the first two issues of John Constantine: Hellblazer, and it would take forever to give any amount of detailed attention to all the callbacks from thos issues. So for all intents and purposes, we're doing Easter eggs on auto pilot tonight.
Let us know if we missed anything that was worth specifically calling out. Otherwise, here's a general overview of what came from the comics, as well as a few additional notes we found interesting.
Gary "Gaz" Lester
In the comics, Gary Lester is Constantine's long-suffering former friend and bandmate. After being possessed by a demon, Lester was consumed and destroyed when Constantine trapped the creature inside of his friend's body and became one of a number of spirits haunting Constantine for years.
Okay, so..."A Feast of Friends."
This episode may be the truest adaptation of any single comic book story this side of occasional episodes of The Walking Dead.
Rather than itemize every little thing about the episode that syncs up with Hellblazer #1 and #2, here's the high points for that issue: Gaz rescues a boy who's got a demon bound inside him, and then heads to John for help when the demon gets out of control. People are being infected by the demon, gorging themselves until they drop dead and then the swarm of bugs (in the comics, flies) that represent the demon head off to a new victim. John heads to an African mystic who says he's been expecting him and gets him high to show him a vision of how the kid got the demon inside and why that's the only way to stop the demon. Constantine, who in the comics has help from Papa Midnite to do so, straps Gaz down and traps the demon inside him, then they wait outside of a cell while Gaz dies and brick it up after he and the demon are gone.
So...yeah. Outside of the fact that the comics have Chas and Papa Midnite and no Zed to be found (she didn't appear for the first time until Hellblazer #4), it's a very, very similar story.
Demon in a Bottle
It could be unintentional that they use the phrase "I trapped the demon in the bottle," but since so much of Gary's trouble starts and ends with his addiction issues, it's worth noting that "Demon in a Bottle" is one of the quintessential Iron Man stories, and deals with Tony Stark's alcoholism.
That dancing pig...
This may be commonplace around the country, or it may just be my brain, but when I saw the dancing pig and cow on that logo, I was brought to mind of the dancing pig in a tutu who serves as the logo for Gianelli Sausage, a local mainstay in my hometown of Syracuse, New York.
I can't find any entry for The Mist in the Hellblazer Wiki, so it seems likely to me that the name was made up for the TV series. In either case, a classic Starman and Flash villain named The Mist recently appeared on The CW's TV adaptation of The Flash.
UPDATE: Anonymous6717 said ... (original post)
The shaman was Doctor Mist.