Ploy passives and minimal resistance

Just saw this on a most useless unit post

33 is the minimum number for me if they're unmerged.

It depends on the mode you're playing really.
In Arena, I'd recommend having at least base 37-38 to ploy most enemies.
In AR, 32 should be enough against most comps, but it goes up to 37 again against tanky comps.
In PVE, 32 works. But not in Abyssal difficulty. There, you don't ploy at all.

34 if my target is Surtr, 32 if not

I say 30 is the absolute minumum, but it'd be better at around 33.

Unless you're using Res Ploy, then I'd say at least 36 or 37.

Don't overthink it. Hit 30.

Res ploy 37+
Def Ploy 30+
Atk/Spd Ploy 35+ (otherwise just run a smoke)

vs non-tank or def-only melee (ex: Ogma, Nephenee): 30 will hit mostly everything. Most likely exceptions: Caeda, Fir, Clair
vs offensively focused mages (ex: Nino, Ishtar, Linde) and healers starting from Maribelle (ex: B.Veronica, H.Mia, Mikoto): 34 is the minimum to hit mostly everything. You might occasionally miss against some Mae or Delthea
vs res tanks (Sheena, Micaiah, Felicia): 39 is the bare minimum I would recommend. Both sides might be trying to ploy the other.

Note how my numbers correspond to Tandor's

In my opinion, the only right answer is enough resistance to ploy the units you need to ploy. So find out which of those units you wish to hit has the highest res, and make sure to beat that.