Flurry of blows interaction with serpent runner

[Gingor]

So flurry of blows allows you to make all of your twf attacks with one weapon, serpent runner decreases the twf penalty for your primary weapon by 1. Would this allow you to lower the penalty on all twf attacks by 1 if you use the same weapon/only unarmed strikes? If not how would it work?

[I grok do u]

Depends on chained monk vs unchained monk (or whichever of these an archetype is based on).
Monk flurry of blows is explicitly "like two-weapon fighting," so serpent runner could apply to the non-bonus attacks.

For unchained monk, two-weapon fighting is not referenced in flurry of blows, so the trait would definitely not apply.

[Gingor]

I grok do u wrote:

Depends on chained monk vs unchained monk (or whichever of these an archetype is based on).

Monk flurry of blows is explicitly "like two-weapon fighting," so serpent runner could apply to the non-bonus attacks.

For unchained monk, two-weapon fighting is not referenced in flurry of blows, so the trait would definitely not apply.

I was specifically looking at the brawler(constructed pugilist) and the jistkan artificer magus, I should have mentioned that

[I grok do u]

Same principle, so it looks like both of those should work. Brawler's flurry references two-weapon fighting again for the extra attack(s), and Jistkan artificer references monk (although I suppose that is open for GM to decide whether that is unchained or not).