Say a PC is attacked by an artifact with a petrification effect, for example, but the PC in question has the UNCHANGING universal mythic path ability, which makes him immune to non-mythic polymorph and petrification effects. Does he get petrified?
Are there mythic artifacts and non-mythic artifacts? Or are all artifacts generally considered to by mythical by their very nature?
That's all GM territory. Nothing in the rules suggests that all artifacts are mythic, but any artifact could be.