So, Shield Trained allows you to treat Heavy Shields as light weapons, which would make a Large HS a one-handed weapon and a Huge HS a two-hander... what would the damage dice of that be if it was also Spiked and had the Bashing enhancement?
Good Question.
Bashing essentially adds two size categories, so this would deal damage like a colossal spiked heavy shield. It starts as medium for 1d6. As large, that becomes 1d8. As huge, that becomes 2d6, and as gargantuan that becomes 3d6. But there is no up-conversion from 3d6 to a new value for colossal.
What to do?
Well, the previous upgrades increase the average damage as follows:
3.5 to 4.5 (increase of 1)
4.5 to 7 (increase of 2.5)
7 to 10.5 (increase of 3.5)
That's not a simple progression either, but based on that, increasing the average damage by 4.5 seems to be on the edge of too small, so maybe increasing the average damage by 5 would seem about right. That brings us to an average damage of 16.5.
We like lots of dice, so that rules out a single d32... ;)
So what has an average of 16.5 and uses at least 3 dice or more? Easy. 3d10. Exactly the average we're looking for while keeping the quantity and types of dice rolled fairly simple.
I can't support that with RAW, but it seems reasonable enough to me...
So, Shield Trained allows you to treat Heavy Shields as light weapons, which would make a Large HS a one-handed weapon and a Huge HS a two-hander...
No. The trait does not say "allows you to treat heavy shields as one category lighter than they are." It says "Heavy shields are considered light weapons for you." That's it. It does what it says it does, but nothing more.
Having said that (my previous post), I don't think I would allow this trait to let people use a shield with 2 hands. That's not how shields are used.
(note: this goes out of the realm of "Rules Questions" and dives deep into the murky waters of RAI)
The trait says "You were trained to use shields as weapons." but I doubt the intent is to pick up a table-top and clobber people over the head with it like it's a giant club - if that is what the trait were for, it would say "You were trained to use tables as weapons."
RAI (or just good old common sense) would lead us to expect the individual to be wielding the shield the way it's meant to be wielded: strapped to one arm. Wielding it any other way turns it into a table-top bludgeon and would probably require a different kind of trait to make any sense - something like "Table-top Trained" if such a thing existed.
Now, a heavy shield is about 3' tall, give or take a little, and a large version would be 2x as tall and a huge version 2x as tall as that - not likely an medium combatant would have a 12' tall shield strapped to his arm. I could believe a 6' shield strapped to his arm. Weird, but he did spend a feat getting extra training to learn to do this and the actual size is not out of the realm of plausibility.
But I think 12' is pushing it too much. At least for my common sense, such as it is.
So, Shield Trained allows you to treat Heavy Shields as light weapons, which would make a Large HS a one-handed weapon and a Huge HS a two-hander...No. The trait does not say "allows you to treat heavy shields as one category lighter than they are." It says "Heavy shields are considered light weapons for you." That's it. It does what it says it does, but nothing more.
Maybe. That's an interesting way to look at it.
But if we full-stop at your interpretation, then a character with this trait could wield ANY heavy shield as a light weapon. Including a colossal heavy shield.
The trait says "heavy shields" (plural) which means some number of heavy shields larger than 1. How many? Well, given your full-stop and the absolute lack of any other limitation within the text, the number is unlimited which means ALL heavy shields. And with no restriction on size, that includes ALL heavy shields of any size. Ergo, this trait lets a gnome wield a heavy shield sized for a colossal titan, and he can wield it as a light weapon.
Reductio ad absurdum, of course. And clearly not what you mean.
Fortunately, we have rules for using larger weapons with increased damage and increased effort. Since a character with this trait treats heavy shields as light weapons, we can apply the existing rules for larger weapons exactly the same way we would apply them if he were wielding a short sword as a light weapon.
(which leads to new absurdities, but hey, it's not the first absurdity in this - or any other - rule set).
It's a normal enchantment that you can add to any shield. Take your +1 heavy shield (enchanted to improve its shield bonus to AC so now its total shield bonus is +3) and add Bashing, and now you have a shield that improves your AC by 3 points as well as getting a +1 attack bonus and doing extra damage when you decide to bash with it.
There are no rules to wear a Large Heavy Shield, so how are you wearing it to use a Large Heavy Shield as a one-handed if you could.Yes there are, it's called Tower Shield, and it already includes the -2 penalty to attack ;)
Not sure that's an applicable example if one still wants to shield bash with larger damage dice.
Tower shield is a -2 to attack - WITH YOUR OTHER HAND - not with the shield. A tower shield is so large you cannot attack with it.
It's pretty damn close, it has the -2 penaly it is one handed and it's larger than a Heavy shield.
The only difference is the AC bonus that it offers.
Oddly enough, if we're following RAW and find some way to wield ridiculously large shield, a human wielding a colossal heavy shield would still only get +2 to AC, even though the shield would be possibly 48' tall.
Larger weapons gain bonus damage dice, but larger armor/shields don't seem to gain better AC.
So a 48' tall colossal heavy shield adds +2 AC while a 6' tall tower shield adds +4 AC.
Now all we need to do is find the rules to let us wield such an oversized shield. Or not, since it won't give us any benefit until we bash with it...