The Improvised Weapon Mastery feat says:
Increase the amount of damage dealt by the improvised weapon by one step (for example, 1d4 becomes 1d6) to a maximum of 1d8 (2d6 if the improvised weapon is two-handed)
The Shikigami Style feat says:
While in this style, you deal damage with improvised weapons as if they were one size category larger. For every style feat you have that lists Shikigami Style as a prerequisite, treat the improvised weapon as an additional size category larger, to a maximum of three sizes larger than its actual size.
Would these two feats stack? And how would it affect the damage dice if used with a frying pan, for example?
Best Answer
No, they do not stack.
The Size Stacking FAQ states:
Improvised Weapon Mastery states:
Which would fall under the similar language portion of the FAQ for effective size increases.
Given that Shikigami Style states:
The clause in the FAQ about taking the highest effective size increase applies, and you would take the larger of the two, which will always be shikigami style since it will be the same or larger than improvised weapon mastery.