|Mathwei ap Niall|
So, assuming we can throw out spiked and bashing (three size categories) and cite the rule that Lead Blades and Impact overlap instead of stack, that leaves us four increments short. The Shield Champion is now only bashing for 8d6 at level 12 (4d6 without that druid magic), and 12d8 (6d8 without druid magic) at level 20. Are there any other interactions we can rule out? I'm hoping for more RAW than RAI here, but I'll take what I can get which is well-supported.
Edit: I would also really appreciate some official address to the language to get rid of the ambiguity.
Since Strong Jaw specifies it only works on natural attacks (which a unarmed strike is NOT) then you can remove those size increases as well.It's also flagged as a size increase so doesn't stack either.