Can the effects of one artifact override the effects of another artifact?
Example: a player has an artifact that makes them immune to Fear and Charm...
Can another artifact override that?
I'd say it depends on the nature of both artifacts.
- Has one artifact shown to be more powerful than the other?
- Is the fear/charm or immunity the primary purpose of one of the artifacts?
- Is one of the artifacts specifically created to overcome the power of the other?
- Were the creators of one of the artifacts more powerful than the creators of the other artifacts?
- Which artifact has the higher Ego score or are the items sentient?
- Who is holding the artifacts?
- Are the possessors of the artifacts doing what the artifacts want?
Let's say the first artifact is the Token of Valor, created by Heironeous himself, and it's primary purpose is to enhance and protect the power and valor of a warrior dedicated to Heironeous or good who battles against the designs of evil deities. When wielded by a mortal of sufficient quality, it grants continuous heroism
(immunity to fear) and a continuous holy protection
(as protection from evil and good
except it additionally protects against creatures of any type so long as they worship or serve an evil deity or power) because the artifact's primary purpose is to bolster and protect those who fight for Heironeous and against his enemies. [For those wondering, I've made this artifact up on the spot.]
The second artifact is the Sword of Kas, a sentient magical weapon created by the lich Vecna, with the original primary purpose of allowing Kas to fight for Vecna, now twisted to destroying Vecna at any cost. Let's say the sword has the power -- among other things -- to cast a combined cause fear
and charm person
(as the spells, but this can affect any creature except Constructs, Plants, or any creature bound to the will of another such as an animated Skeleton or Zombie or summoned creature).
Now, let's say a Paladin of Heironeous bearing the Token of Valor confronts a Blackguard of Erythnul wielding the Sword of Kas. The Blackguard throws his charm/fear whammy. What happens?
Has one artifact shown to be more powerful than the other?
Well... The Token of Valor was apparently created to do a very simple, albiet potent, thing. However, the Sword has a laundry list of other powers and abilities, as well. The Token is, well, undefined or unknown. The impact that Vecna and Kas has had on Oerth probably makes it the more powerful artifact. The sword has more influence in campaign world history, therefore the Sword probably has more power. Winner: Sword of Kas
Is the fear/charm or immunity the primary purpose of one of the artifacts?
The immunity is the primary purpose of the Token. The paladin worships Heironeous and is battling against evil. These powers are the only ones known, possibly the only powers at all. On the other hand, the whammy is not
the primary purpose of the Sword. The blackguard is neither Kas himself nor is she trying to further the cause of destroying Vecna. Winner: Token of Heironeous
Is one of the artifacts specifically created to overcome the power of the other?
Hm. Debatable, but not really. The Token is focused on overcoming evil deities, not the Sword. The Sword is focused on Vecna. Unless the Blackguard is doing the will of Erythnul, there's nothing specific here. Winner: Tie
Were the creators of one of the artifacts more powerful than the creators of the other artifacts?
The Token was created by an intermediate deity. The Sword was created by an absurdly powerful, undead, but still not immortal lich at the peak of his undead power (and who later became a lesser deity). The token has the potential
to be more powerful here, simply because Heironeous is more powerful than Vecna has ever been. Winner: Token of Heironeous
Which artifact has the higher Ego score or are the items sentient?
Only the Sword is sentient. The Token has no appreciable intelligence, though it may influence the actions of the bearer. The Sword is known to take over it's bearers. In a direct contest of wills, the Sword would probably win in spite of the powers of the Sword. If you had two sentient artifacts, you could consider a contest of wills between the artifacts themselves
to resolve the issue if it makes sense for the story, but here it doesn't make sense. Winner: The Sword of Kas
Who is holding the artifacts?
A Paladin of Heironeous, and a Blackguard of Erythnul. Winner: I call it a tie, but it might favor the Token
Are the possessors of the artifacts doing what the artifacts want?
Well, we don't really know much here. We know the Paladin is fighting evil, and the Blackguard is fighting good. The Paladin sounds like he's doing what the artifact was created for, while the Blackguard is kind of doing her own thing and just killing everything... but that's kind of her purpose and the Sword gets awfully thirsty as I recall. Winner: Tie
Here I say the Token is slightly favored perhaps. If Kas was holding the Sword we might have a different answer. If a Paladin of St Cuthbert held the Token of Heironeous we might also have a different answer.
Remember, the power of artifacts is that the fluff carries more weight than the crunch