That was done by tricking the AI coding by doing really specific things. He's obviously talking about actual fights with them.
And I personally agree with him, LV 9 CPUs outside of the screw ups, are actually the most challenging to me. I had a much easier time with the LV9 CPUs in Brawl and SSB4 3DS. Seriously, those event matches... brutal
Yeah, I don't know how they code their cpu, but they are so good that they only need a simple parameter to change so much factor.
Like, for example, the codec FLAC, you only need to furnish a number between 0 to 8 to determine how much you want the files to be compressed (still lossless tough). This is kinda similar except it changes a whole cpu behaviour and the numbers represent very well their behaviour.
Like, I'm sure they have tons of properties that are all influenced by this such simple number that studying it shall be crazy and interesting. Like, the classic mode having to the decimal ...really it's genius because it's such a simple system to use and it's so powerful.
What I'm wondering is how they figured this system out? This is present in almost every game Sakurai made and even where he was with HAL and even kirby air ride has it so it just got adapted.
I don't know, but for such a simple UI, it does so much.