Is this something someone need to make a separate acc for? Cause vast majority of the time this won't be the 1st post of anyone... Anyhow.
"A Boy and His Orc/Slime" rule of:
Assuming you have one "average"... Wait, that doesn't exist... One unskilled
non-specific PC (think of s/he as a peasant/tourist class.) character at basic abilities (eg. Lv1).
On the other hand you have your baseline monster. - Western RPG it'd be Goblin or Orc, JRPG usually a slime. - Whatever is fine. It is supposedly a beginner-based monster with no surprise nor overkill. (Seriously, the point is to not
pull any Goblin-Slayer level Goblin Master Race crap here... UNLESS the point is exactly that, but in that case that'd be a whole different mechanical question otherwise.)
1) How difficult should it take our peasant to slay our monster?
2) How much effort it would cost our peasant to slay our monster?
3) How long would it take our peasant to slay our monster?
>Note the whole idea is that the basic PC should be able to slay the basic monster aside of crit/fumble situations. If that isn't the idea, adjust parameter to your needs.
>Special abilities are intentionally not included. Cause them being "special" means anyone without that particular "special" would be unable to be included in the formula ie. They're completely not designed to run with that monster. That type of monsters are usually reserved for boss-type or medium-high+ difficulties, throwing that at your beginner PC is about the same as trolling them (actual trolls monsters not included.)
Also avoiding SP-abilities at this time means you don't need to always have a uniquely-specific "rote" to deal with it, of which again are usually reserved for boss or medhigh+ types. It makes things more unpredictable and dealable instead of "f__k I can't win so I might as well not play" reactions.
>"Not scaring your players" is not included in the question. It's also kinda unanswerable in specific ways as well.
Those are the questions you need to answer for yourself. This is the basis of how brutal you want your game to be.
Once you figure that out,
1) Take your basic monster.
2) Try the same thing with all your basic classes at Lv.1 capabilities. Note what happens.
And the when your done, get other people who have enough idea about your thing to do a blind dry-run through ii) and see if your estimate fits general perception.
(If you don't have anyone, the it depends on how good you can think like other people... Not impossible, but harder than one might think.
From then on, you can gradually:
>increase abilities for both monsters and PC-classes
>increase numbers involved on both sides.
>Change monsters to other types. It might not be a "one can handle one" situation anymore, but you still have to have a general idea for what happens.
>start throwing in "rote-required" monsters and see how all classes handle them.
If you are not designing all the way down to the foundation:
Get your estimated generic PC to designated level instead of Lv1. Other stuffs would be the same.
And you can gradually adjust the outcome as you see them.