Gangs of Sherwood

Artifacts are temporary buffs that you find in blue chests throughout the game. They last for the duration of the current mission you're playing then go away afterwards. They are also complete RNG and you can have the misfortune of getting the same artifact several times in one mission, and no, they do not stack.

I have compiled a list of artifacts for you all below. Keep in mind, Brilliant Amethyst Gem, Sturdy Ruby Gem, and Royal Wine are EXTREMELY rare pickups when playing solo, but I did manage to see them a little more often when playing co-op:

Brilliant Amethyst Gem (Rebel Instincts last longer)
Sturdy Ruby Gem - (Rebel Instinct segments charge faster)
Knights Chain (increases defense by 30%)
Executioner's Gauntlet (Finishers can be done faster)
Royal Wine (abilities recharge 15% faster)
Golden Horseshoe (increases critical damage chances)
Bloodletting Fleam (attacks slightly heal you)
Golden Tooth (attacks become uninterruptible)
Silver Rosario (grants 1 auto revive)
Dragoon Medallion (adds 60% damage to launched enemies)
Blacksmiths Flint (adds Burn damage to attacks)
Jester's Marotte (grants Enraged)

The last two can ONLY be found in co-op:
Elite's Mead (revives are 50% faster)
Jester's Bell (enemies become aggro'd to you)