Bloody hell! I knew it would be hard but that's insane! lolDefine "good spread".
These are rough calculations to give an idea of numbers ('cause lazy).
The odds that the random IV falls in one of Attack or Special Attack (assuming you're ok with 5IV spreads) is 1/3.
You have 1/512 chance of getting a shiny on your own save (assuming MM parents and Shiny Charm).
There's an additional 3/4096 for the other three (since the Shiny Charm and MM parents don't work towards helping those saves).
So if that's "good" then 1/3 * (1/512 + 3/4096) ≈ 1 in 1120.
If you want the random IV at 31, then there's a 1/32 chance of that. Shininess stays unaffected so 1/32 * (1/512 + 3/4096) ≈ 1 in 12,000.
But yeah, that's exactly what I wanted to know, thanks! :)
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Final random question: Does anyone have a link to an up-to-date list of Pokemon that can't have their Hidden Abilities yet? Thanks in advance! :)