The Hammer of Thunderbolts is described as a +3 Large returning warhammer according to the PRD.
I am a human barbarian and after a horrendous quest line our party was rewarded with a few things. One of the things I was rewarded with was the Hammer of Thunderbolts. Being a medium creature, and the hammer is large, I see that I can take a -2 penalty, but... the Armor Class of the things we are fighting is so high, I can't really afford a -2.
A search on the PRD came up empty for me. I have spoken to the GM, since I have a Belt of Giant Strength already - and he said we can see about making a custom item. The custom item would be similar to the 3.5 Strongarm Bracers, but would instead be gauntlets - akin to the gloves that Thor needed to lift Mjolnir.
Custom item creation aside, what can I do within the existing rules to negate this penalty? My next level will give me a feat.