I am starting this tread to hammer out some of the details for Inappropriately Sized Shields House Rules since there are no official material around on this subject.
Please keep an open mind.
Here it goes.
A Medium sized Heavy shield may be used as a large sized light shield with -2 to shield attack rolls and an extra -2 to ACP to the shield.
A Small sized Heavy shield may be used as a Medium sized light shield with -2 to shield attack rolls and an extra -2 to ACP to the shield.
A large sized light shield may be used as a Medium sized Heavy shield with -2 to shield attack rolls and an extra -2 to ACP to the shield.
A Medium sized light shield may be used as a Small sized Heavy shield with -2 to shield attack rolls and an extra -2 to ACP to the shield.
A buckler and tower shield is only designed to work with a creature in which it is sized for.
Example: A Small sized buckler is too small to provide any AC to a medium size person.
Example: A large sized Tower Shield can not be used by a Medium size person because it is too big and heavy to wield.
One may use Effortless Lace with a heavy spiked shield to make it a light weapon.
(NOTE) Effortless Lace must still be used with a one-handed piercing or slashing melee weapon. The "grips" part may be arguable.
One may remove the -2 to shield attack roll with an Effortless Lace, but not the -2 to ACP.
(Note) That spike shield and Bashing enchantment are both Size bonus and do not stack.
Now for the storm of criticisms and comments of rule and game breaking.
What if the medium sized creature wielded the large tower shield in two hands? Probably still too large, because a large creature is more or less 8 times the mass of a medium one, but that would at least follow the rules for weapons of different size.
I think it would be good to have this stuff clarified, but honestly this has never come up in a game I ever played.
Doesn't happen to me often. But there was one time when a halfling rouge used a medium size heavy shield from a fallen teammate to use as cover against mass attack of arrows and we used tower shield rules for the size different.
It was one time, but now the group has noted that there's no rules or anything really on Inappropriately Sized Shields and we are "Discussing" what is the best way to handle it.
This is my first try at it.
I can now see that I poorly explained myself. Let me try this again.
If you are using an Inappropriately Sized shield as a weapon only, use the standard Inappropriately Sized weapon rules and the shield wouldn't give you any Shield bonus to AC.
If you are using an Inappropriately Sized shield as a shield you would incur a -2 to shield attack rolls and an extra -2 to ACP to use the shield, but keep the Shield bonus to AC.
The Shield bonus to AC is based on what the kind of Shield it counts as toward the wielder. +1 for light shields and +2 for heavy shields.
The -2 to attack rolls for using an Inappropriately Sized shield is the same -2 to attack rolls for using an Inappropriately Sized weapon.
The extra -2 to ACP represent how awkward it is to use an Inappropriately Sized shield. Odd sized grip and straps.
Bucklers and tower shields can only be used by a creature in which it is sized for.
Damage would be based on the what the kind and size the shield is.
Type......S.......M.......L..
Light....1d2...1d3...1d4
Heavy..1d3...1d4...1d6
A Large sized Heavy shield counts as a Medium sized Heavy shield with -2 to shield attack rolls and an extra -2 to ACP to the shield.
The damage of a Large sized Heavy shield would be the same as a medium sized Heavy shield.
What would be the point? There may be situations where the only gear available to you are the wrong size. There are rules for weapons but not shields. Armor must be sized to you. Period.
A Large sized shield for a medium sized person when trapped by giants. Or Specific Magic Heavy Shields for small sized person used by a medium sized person. Etc.
I know this is wordy, but I am doing my best to articulate my thoughts on this subject. Hope it helps. If not, I will try again.
Yep, you're right. Typo.
The damage of a Large sized Light shield would be the same as a medium sized Heavy shield.
Gallant Armor wrote
"I think -2 to shield attack rolls and an extra -2 to ACP for medium creature wielding a large heavy shield sounds fair."
The only way this could work if you use tower rules or wield 2h as stated by Inappropriately Sized weapon rules. A large sized heavy shield may be to big to be wield by a medium creature.
Tower shield rules would be:
+4 to AC or cover, some conditions apply.
Max Dex 2, -10 ACP, -2 to all attack rolls because of the shield’s encumbrance.