Champion Spawn Artifacts
Most of the useful Champion Spawn Artifacts ("equipment") are referred to as Replicas, because they are near copies of items handed out at Event Moderator events, with the word "replica" in the name to differentiate them from the originals. Some items do not match their counterparts exactly, perhaps having different intensity bonuses or Durability stats. No Replicas have the Self Repair property regardless of whether the originals did or not, and Powder of Fortifying cannot be used on them.
Most non-Replica Champion Spawn Artifacts are decorative in nature.
Confusingly, the Stygian Abyss expansion introduced a number of useful Champion Spawn Artifacts that were not Replicas, as rewards for doing the new Champion Spawns, yet also added new Replicas.
There is a 30% chance that a Champion Boss will drop any of the following. Out of that 30, there is a 5% the drop will be unique, 10% the drop will be a shared item and a 15% chance the drop will be a decoration. The items appear directly in your Backpack and do not need to be looted from the corpse of the dead champ.
Your chance of receiving an artifact is supposedly based not only on how much damage you did to the champ, but also on how much damage you did over the course of the spawn overall. In theory, players who turn up solely to battle the champion at the end of the fight have only a minor chance of receiving a reward. The damage counter for a given character resets when the champion of the current spawn dies. If you do not have enough room in your pack for the reward, or are not in the spawn zone when the champion dies, then you will forfeit your chance of receiving an artifact.