So a PC is using a light-mace equivalent improvised weapon and becomes the recipient of an Enlarge Person spell. Does her Improvised Weapon Mastery feat no longer increase the damage of her weapons?

(from the PRD:) 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)

So a PC is using a light-mace equivalent improvised weapon and becomes the recipient of an Enlarge Person spell. Does her Improvised Weapon Mastery feat no longer increase the damage of her weapons?

(from the PRD:) 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)

...I'm sorry, I don't quite follow that. Wouldn't that mean then that, since the current size damage is 1d8 already, the feat would _not_ work (in terms of damage steps)?

Let's take it step by step:

Step 1) PC picks up chair leg to wield as a weapon.
Assuming a medium sized PC and the mentioned feat, you have a medium sized improvised weapon dealing 1d8 damage (19-20/x2 crit).

Step 2) PC receives a casting of Enlarge Person.
According to the wording of Enlarge person, all your gear increases in size with you. Because of your feat, your chair leg was a medium weapon dealing 1d8 damage. When you got enlarged, your weapon grew in size, going from 1d8 to 2d6.

Step 3) ...

Step 4) Profit?

The reason this works is because the feat says that the improvised weapon itself increases in a damage die, not that you treat improvised weapons as if they were one damage size larger. So you have a medium 1d8 weapon which becomes a large 2d6 weapon. Think of it like stacking bonuses. Improvised Weapon Mastery adds an untyped (or "feat" bonus if you'd like) and Enlarge Person adds a "size" bonus. Since players can add bonuses in the order most advantageous to them, it works.

If the wording of Improvised Weapon Mastery stated that you treated the weapon as one size larger but only up to 1d8 or something, it wouldn't work.

If the wording of Improvised Weapon Mastery stated that you treated the weapon as one size larger but only up to 1d8 or something, it wouldn't work.

It's a very pedantic difference but hold with me.

The feat says "Increase the amount of damage dealt by the improvised weapon by one step". Had it said "Treat the weapon as if it were one size larger for the purpose damage" then it wouldn't stack with Enlarge Person. Because the improvised weapon's damage die actually increases (rather than being treated as if it increases), it stacks.

Yeah, it's splitting hairs, but that's how RAW works.

It's a very pedantic difference but hold with me.

The feat says "Increase the amount of damage dealt by the improvised weapon by one step". Had it said "Treat the weapon as if it were one size larger for the purpose damage" then it wouldn't stack with Enlarge Person. Because the improvised weapon's damage die actually increases (rather than being treated as if it increases), it stacks.

Yeah, it's splitting hairs, but that's how RAW works.

What if I am a huge giant with the feat? Do I not benefit because the base damage of my improvised huge weapons is already so high?

The base damage of an improvised weapon is not based on your size, but rather the size of the object you choose to wield. If a human were to pick up a chair leg (roughly the size of a medium light mace) it would do 1d6 damage. If a cloud giant were to pick up the exact same chair leg, it would do 1d6 damage. However, this cloud giant could also decide to wield a decent sized oak tree as a weapon instead. That would do considerably more damage.

The way that Enlarge Person works is that, in addition to increasing the size of the character, it increases the size of their gear. This takes your medium light mace and makes it a large light mace, which increases the damage by one step.

The text of Improvised Weapon Mastery sets a cap on what it can increase the damage of improvised weapons to. If your cloud giant picks up a tree and you rule that it does a base 4d6 damage, then your cloud giant would not benefit from the feat. On the other hand, if your cloud giant picks up a chair leg with a base 1d6 damage, it would receive the damage increase to 1d8.

The base damage of an improvised weapon is not based on your size, but rather the size of the object you choose to wield. If a human were to pick up a chair leg (roughly the size of a medium light mace) it would do 1d6 damage. If a cloud giant were to pick up the exact same chair leg, it would do 1d6 damage. However, this cloud giant could also decide to wield a decent sized oak tree as a weapon instead. That would do considerably more damage.

The way that Enlarge Person works is that, in addition to increasing the size of the character, it increases the size of their gear. This takes your medium light mace and makes it a large light mace, which increases the damage by one step.

The text of Improvised Weapon Mastery sets a cap on what it can increase the damage of improvised weapons to. If your cloud giant picks up a tree and you rule that it does a base 4d6 damage, then your cloud giant would not benefit from the feat. On the other hand, if your cloud giant picks up a chair leg with a base 1d6 damage, it would receive the damage increase to 1d8.

Then the giant doesn't waste a feat on it. It's like saying that metamagic feats are unfair because single-classed fighters can't use them. To paraphrase a quote from James, "Not all feats are equally valuable to all characters." The cloud giant is already dealing 4d6 damage when wielding his improvised oak tree club. Tack on his massive strength and very good to hit bonus and I doubt he'll miss the little bonus of upping his d6s to d8s.