How to build-craft...

[Antorius]

...without just looking up OP, cookie-cutter build specifics?

A typical run starts like this in my head, pretty much irrespective of weapon...

Playing "for real": Athena keepsake for dash

Playing "for fun":
- Keepsake for theme (e.g., full lightning); or
- Keepsake for personal challenge (e.g., Butterfly or Plume); or
- Shackles for random

...and then -- apart from basic ideas like prioritising stacking damage/curses on fast weapons such as Stygius (Zagreus) or Malphon -- I just sort of see what happens, and try to make the "best" decisions as I go (but my reasoning is surely flawed).

How should I be planning my builds? Are there core builds, and/or core principles for build-crafting? What sort of rationales should I be applying, and why?

[The Queen Salis]

I never start those runs with a specific god keepsake. I take the coinpurse.
I will meet some gods in Tart, pick the best boons for my weapon and playstyle, then after defeating the boss, I would swap for a god-trinket according to "what boon I think would be a neat addition here" Repeat that before Elysium, and for Styx it makes more sense to take a combat trinket of some sort.

Adapting to your initial Tartarus draw is better than trying to craft from the start because you get the starter cash XD

I play with Fate persuasion and money accumulation Mirror upgrade, so early cash really helps me build a ridonkulous money pile for the final shop.
Every so often you get a chance to purge boons for some cash. I always consider that and would use my re-rolls there to pick better.

[Paranoia]

I second the motion that starting with a god Keepsake is not really what one would be doing, unless trying for some specific prophesy, dialogue, or something. The Coinpurse is the best if one is still trying to unlock things.
After meeting two or three gods, swapping into a god Keepsake for floors 2 and 3 is pretty good for finding proper support for the Boons one already got.
Last floor is then usually something that will help against the final Boss. Or another god Keepsake if I really need something. Usually not, but anyway.

[Antorius]

Thanks for the replies. Hadn't really considered the Hypnos keepsake before! It rolls nicely into the Charon keepsake for momentum through Asphodel or especially Elysium.

Also swapped a couple of mirror abilities from their defaults -- to increased chance of hammers/boons/coins and re-rolling boons/wells instead of re-rolling doors -- and seeing how that goes. Seems encouraging so far...

[Paranoia]

The Charon Keepsake is definitely the most fun. Having two x5 Trap damage Boons and having the final boss die to their own traps is hilarious. And pretty much all of them are very good if one can find them on the last floor.

[Nibbie]

I'll occasionally start with a god keepsake if I know for sure I want that god for that run, so I have the best chance of getting the specific boon I want and can even start poming it immediately; Zeus for attack on the gun would be the most common example. Swap to something like the coin purse for the second area to get the immediate bonus, then something actually useful for the third and fourth areas which are the challenging ones.

In general though, "just sort of see what happens, and try to make the "best" decisions as I go" is the general strategy for pretty much all roguelikes. The only thing to learn is how to pick what the "best" decisions are, and that is at least somewhat subjective, especially in an action game like this. There is no point in using the statistically best build if you can't utilize it properly, and using an unoptimized build well will still produce wins. Unless you are shooting to complete the top difficulties or something, you can really just feel out what combinations of weapons and boons you like and get better at using them. I beat my 32 heat run first try with the Hades Spear, which is usually fairly low down on tier lists, but it is my favorite and most comfortable weapon since I unlocked it.

[Antorius]

Haha that's my favourite and most comfortable, too (also grats on heat 32!)