I'm hoping to implement Automatic Bonus Progression in my upcoming game, but I'm a bit confused about it. In particular I'm having difficulty with the following section;
Any weapon, armor, or shield special abilities on attuned items count against a character’s enhancement bonus from attunement. To determine an attuned magic item’s enhancement bonus, subtract the cost of its special ability from the enhancement bonus granted by attunement. (This applies only to special abilities whose cost is equivalent to an enhancement bonus, not to those that cost a flat amount of gold pieces.) For example, if a character with a +3 enhancement bonus from weapon attunement wields a keen scimitar, she subtracts 1 point of her enhancement bonus (for the cost of keen), leaving her with a +2 keen scimitar. If a character doesn’t have enough of an enhancement bonus to afford the special ability (such as a 4th-level character with a vorpal longsword), she can still use the weapon’s power on its own, but the weapon gains no enhancement bonus.
I'll use an example to explain my understanding.A 9th level character (having a +2 weapon attunement) picks up a keen scimitar and when using that scimitar she must subtract the cost of keen (+1) from her attunement enhancement bonus, therefore leaving her with a +1 keen scimitar. Yet the same character can pick up a vorpal longsword (+5) and still take advantage of the special ability (vorpal) even though they cannot subtract the full cost from their attunement bonus.
My take-away is that the character is paying off the special abilities as best they can, thus possibly leaving them with a weapon with no enhancement bonus but still with a usable special ability. Am I understanding it correctly?
As a follow up, what about Masterwork weapons? The rules state:
In this system, magic weapons, armor, and shields never have enhancement bonuses of their own; those bonuses are granted only through attunement.
Masterwork aren't magic, but they provide an enhancement bonus. Is that removed as well, or does this enhancement bonus persist until a character reaches 4th level and can properly attune to the weapon?