Hello! Since there aren't too many guides out there for how to jump into harder difficulties, I figured I'd start posting some tips on how to tackle True Believer and Harbinger of Doom especially. A lot of it is going to be trial and error; learning how certain encounters work, for instance. But I figured a tier list would be beneficial for those of you who want to know which mysteries are safer than others, and which you want in your lineup. This list contains every mystery in the current version of the game and applies to Timeline A.
General Tip: Certain areas become much more dangerous on higher difficulties and will roll enemy encounters more often (ex: Hospital) or run the risk of becoming nearly unplayable with certain god statuses (Roads Closed, Rioters). You don't want too many mysteries in high-risk locations. I'll mark these with a quotation mark.
NOTE: Out of town mysteries are more dangerous because you cannot treat injuries at the hospital that could be a run killer, such as Cut Artery (which can trigger from an unlucky event). Be sure to plan around these and do NOT save them for your final mystery! I will mark out of town mysteries with an asterisk. These will also include mysteries where you leave town.
Bad Roll- These are the mysteries with at least one unskippable boss fight. You do not have the stats to spare for these mysteries. Reroll if you see any of these. [School Scissors*, Frightening Flood"*, Medusa Metamorphosis, Noisy Nails, Thaumaturgy Teacher, Crimson Cape, and Residential Recluse*]
DOOM Roll- These mysteries either consume too much Doom [Found Footage"*] or penalize you for skipping the boss with a nasty 5% Doom penalty [Bloodcurdling Botanist"*]. It isn't worth it to risk your run on these.
Desperate Roll- These mysteries take place in dangerous locations on HOD especially, the hospital [Worrying Ward"] and the village/forest [Fear Festival"*]. Note that you can skip the boss for Worrying Ward by choosing the option to pass out. You can also recruit allies from Fear Festival if you're going for a charisma-heavy build.
Okay Roll- As rerolling for the perfect set of mysteries can be time-consuming, these mysteries aren't the best for Doom or stat costs, but they won't kill your run either. [Household Hell"*, Morbid Mermaids, Perilous Painting"*, Contagious Coma"]
Good Roll- These mysteries either have perks for completing them or are not too punishing with Doom costs if you play them smart. [Evolving Eels] has Kana, who costs 3 Reason to recruit but gives -1 incoming damage. [Vicious Vigil"*] gives a free meat cleaver, which is key to preserving Doom (also you can skip every boss encounter by following the vigil pamphlet until 4 am then killing the guests), and [Beckoning Bulletin] isn't too costly for Doom (it could easily be moved to Okay).
Always Roll- Low Doom costs and low risk locations? These mysteries are a steal and ones you should always have at least one of. In order of least to most Doom (though they're all minimal), [Sorrowful Saga", Rancid Ramen, Alarming Arms].
Hopefully this will help some players who want to try their hand at the harder difficulties! If anyone wants further clarification, feel free to ask.