Fox boss is a bit trickier. Typically level doesn't matter as much as gear/build in Nioh, but being under-leveled against the fox is rough due to the health pool and damage output. If you have a Guardian Spirit with a long living weapon uptime (ideally earth), that can also help in tandem with...
Most humanoid enemies are pretty vulnerable to the Daiba-Washi spirit skill on Way of the Samurai (if you have the Guardian Spirit Talisman in the Omnyo trees use that; otherwise, use the Moment Talisman loot items). It'll blast people up in the air and let you get a free ground stab or combo...
Did some more investigations. These were my results:
GOOD STYLE (mid P & mid K)
-Hayabusa
-Ayane
-Hitomi
-Bass
GOOD STYLE (mid P or mid K)
-Phase 4
-Hayate
-Rig
-Tina
-Mila
BAD STYLE (mid P & mid K)
-Marie Rose
-Leifang
-Bayman
Then there's Kasumi, who is in a category of her own. Her expert...
depending on whether they intend it to combo into the air toss. Environmental combos are generally bonkers in 6 (bad stage design), and 5U Leon was obviously the king of bonkers environment combos.
TL;DR: Potentially, easy access to lots of air combos into lots of stuff for big boi damage...
@Onryoki In 5, Leon could only get his air throw off on certain weight classes from certain launchers at specific threshold levels. For example, 9K could only lead into an air grab on midweights at Crit. level 3 (same applied to 4PK, I believe). The change to launch heights in 6 normalizes that...
"Dumb" can mean a lot of things. If you're talking about the characters that require the least amount of effort to reach competent performance, Diego is your guy hands-down. Honorable mentions: Kokoro and Hayate