jdunson brings up a really interesting point in the original All Fired Up post:
Something like an "Aura of Flame" might well be a multiplier; "Increases all flame damage by +200%". Some cases might provide base damage as well, some not.I had been thinking along similar lines about a number of related effects. Now I have a flexible way of representing multiple scalars (pvals) on an object in Unangband, I'm inspired to immediately extend the types of bonuses that can be represented.
I've already included context specific combat bonuses: to-hit, damage, number of blows/shots, damage multipliers, range; for melee, ranged weapons, throwing, traps, unarmed combat. This addresses the design problem I outlined in Throwabow: if you throw a bow with a high damage bonus, do you inflict the extra damage?
(Aside: I can immediately see from the above, that I need to include context specific damage dice and sides).
What other interesting bonuses are there?
jdunson's 'boost all fire damage by 200%' suggestion is actually more complicated than it initially appears, because of the number of different ways fire damage can occur - as I outline in Different Ways of Killing. There's weapons, spells, magic items (rods, staffs, wands), thrown oil and fiery potions. Do I also boost damage from a flask of oil (or another fire damage source) set in a trap? Does the bonus boost allies fire damage (which in Unangband is treated as equivalent to damage from the player)?
And for effects, such as spells, which persist over time, does the damage boost still apply if the item is removed?
For those bothered by my repeated mention of Team Fortress 2, the way damage effects apply there is another excellent example of unintended consequences of any of the above decisions. At the moment, TF2 has an example of a damage nerf (the Detonator) which is a secondary weapon which only does +35% damage against burning opponents, unlike the weapon it is based on (the Flaregun) which does +200% damage in the same situation. However, if you switch away from the Detonator before the projectile hits, the game no longer applies the nerf, and so you get the full +200% bonus. TF2's history of bug fixes is littered with this kind of interaction (damage bonuses against aerial opponents if they are merely standing on stairs and so on).
So I believe I'm better off by focusing on the context of the damage bonus, and then designing weapons which list the possible related contexts. To take an example: I could add boosts to casting spells by increasing the effective level of the player casting the spells, the effective level of the player when learning spells (which makes more spells available), the failure rate of spells and the casting cost of spells. In addition to a general boost, I could also add spell book specific boosts. A sword of fire would then list each of the above boosts which regards to the fire spell books, along with the relative minimum and maximum values; and when randomly generating a sword of fire item, specific values are chosen.
This does become a problem for the player to compare weapons - which is already a major issue, but hopefully the bonuses are going to be concrete enough to make a comparison (Do I want to be able to cast fireballs, or get an extra +x1 damage multiplier?).