Get between -10 and +20 acc over res.

Yup yup.  There's a chart you can find online but usually I shoot for +25 to enemy RES.  IIRC that's roughly 96 - 97% to land.

Here it is, the horizontal line represents the difference between accuracy vs. resistance, the vertical line represents % of success

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Note that you can get 3%'ed either way. Someone with 0 accuracy will land debuffs on you 3% of the time even on a 1000 resistance Mithrala. And inversely, your 800 accuracy Madame Serris will fail to strip a 100 reistance nuker 3% of the time, as examples.

I saw this online.  They referred to X and Y axis but neither were labeled.  

Is the 3% RNG related?

Well yes. As you can see on the chart, the curve never touches the 0 or the 100 on the Y axis. Those are the two 3% areas.

Just like the built in house advantage in casinos.  lol

Plus 30 on Acc is as good as it gets.  

Thanks for the info.  

It's a question of limits. The curve converges on 3% / 97% as x approaches infinity on either side. Practically speaking, what that means is you get diminishing returns trying to get results below 5% and above 95%. Hence, aim for acc between -10 and +20 of res, and aim for res about +50 of acc.

Offensively speaking, i've never experienced trouble with my guys landing abilities even if i built them not to, except in one case.

I had built an Alsgor / triple PK / Geo team to run IT15, pretty much the same as Helicath's. Trouble is, before building it, i went ahead and ascended Alsgor to 6, thinking the banner would help me get to the required speed. The bad trade off was that I unlocked the passive that can put decrease speed on boss. Even with 0 items with accuracy, the length of the fight meant the boss could eventuaaly induce the passive to land, and if it landed on the wrong Alsgor turn (i.e. immediately after having put block damage), game over.

In this instance, the 3% was super annoying. That comp could fail at least once if not multiple times each day just because of that.

I've rebuilt my team to go with Emic instead, 99% win rate. And much faster too.