I recently was made aware of the new hybrid classes and decided to give them a look, as my players had expressed some interest in playing them. I was promptly gobsmacked at what I saw as a nightmarish oversight in handling die size scaling thanks to Close Weapon Mastery in the brawler, and in the Shield Champion in particular. Those who wish to ignore the numbers and just quote me the rules that say this is not possible, if such rules exist, skip or skim the following:
1. "At 12th level, a shield champion can use her unarmed strike damage when dealing damage with a shield (whether in melee or thrown) or the shield's damage, whichever is greater." At this level, that's 2d6. A non-shield champion brawler will be dealing 1d8 instead, as the shield bash is in the Close weapon group.
2. Shield spikes increase the size rating of the shield by one category. For the SC that means a 3d6 shield. For the standard brawler that's a 2d6 shield.
3. Bashing property increases the size rating of the shield by two categories. That means the SC goes from 3d6 to 6d6. Standard brawler goes from 2d6 to 4d6.
4. Using a heavy shield means it's not a light weapon, and thus qualifies for the Impact enhancement, increasing its die by another category. SC goes from 6d6 to 8d6, standard from 4d6 to 6d6.
5. Enlarge Person and Lead Blades (external augmentation), both of which are found cheaply in wand and potion form. These are worth a size category each. Enlarge Person does have a caveat stating that multiple magic effects increasing SIZE do not stack, but says nothing for size categories. It is the only effect listed that actually increases your size. RAW, both work. That's two more increases, taking the SC to 16d6, the standard to 12d6. Per bash. At 12th level.
6. Strong Jaw, contingent on having a druid or ranger in the party, or access to significantly more expensive wands or potions. Two size increases. 16d6 goes to 32d6, 12d6 goes to 24d6. This one works on the base damage that the shield is set to (that of the unarmed strike), but these can generally be added sequentially for the sake of figuring out the die size.
With all of these shenanigans in play and available to, say, a fighter, the shield bash would only be a 6d6 weapon. That's still nothing to sneeze at in standard play, but 12d6, 16d6, or even 24d6 or 32d6 are just absurd at any level of play. Carrying my scaremongering on from here, at 20th level that Shield Champion would be doing 48d8 + Str mod, per bash, getting seven bashes per round on a full attack.
So! This is me seeking clarification on rules, an official statement addressing possible errata if errata is missing, or some other form of encouragement.