Extremely Critical to Plot << WATCH "All This and Gargantua 2" special BEFORE starting season 6.

Further notes: Halloween was released as a teaser before the season start after a long delay between seasons (2 years), technically watching this up through 10:53 (end of second chapter) then Halloween, then the rest of this (picking up at start of chapter 3) would be the right chronological order.

Critical to Plot << (Watch BEFORE Episode 2 of season 5!!)
May contain spoilers. Chronologically takes place after season 4 -DURING- the events of S05E01 as a self-contained side adventure unrelated to the main plot. Events at the end of S05E01 reference happenings during this episode.
Was released between seasons as a teaser and because of the long wait.

Chronologically takes place before Halloween special and therefore before the end of S5 ep1.

AI Upscale from DVD to 4K (HW not CPU/software) then CPU re-encoded/scaled down to 1080p. Looks fantastic compared to source and much better than Amzn's upscale.

Technically the most absolute correct chronological order here is: this episode > then "From The Ladle To The Grave The Shallow Gravy Story" (Rusty learns a certain fact about another character in that and already knows it by Halloween special) > then start watching S5 ep1 premiere, stop it at 10:53 (end of chapter 2 before start of chapter 3), > then put on Halloween special, watch it, > finally resume watching S5 ep1's from the start of chapter 3.

However failing that (stopping and starting episodes in the middle) Halloween should be watched before S5 ep 1 as that's how it came out originally on Adult Swim and "Shallow Gravy" -can- be watched at a later point as though it has one small revelation about a character it's not that important and almost nothing will be missed during watch of S5 due to missing it. Shallow Gravy does have spoilers and references for this episode (P.R.O.M.) so should not be watched before.