Dunidle Legendary Artifacts can be gotten by defeating any of the 10 bosses that appear every 100 levels. The first boss is the Trol and should drop one upon defeating for the first time. If you want the rest of the 4 artifacts than your going to have to farm the boss and beat him multiple times.
It should drop a new artifact with about 1 in 10 odds so you’ll have to retry about 30 times to get them all. Just keep starting at 91 and playing through until you beat the boss and eventually they will drop them all.
Once you win against the boss you have the option of Restarting which means you start over at stage 91 with full health and run through to the boss again. This is a good option for farming and is an indicator that they would drop something else. Your bonus gold will stack up in the background even though it doesnt show while restarting many times. Getting them right when you can beat the boss is the best so when you have to restart than you will have more of a boost for going through again.
You can miss the artifacts on the first play through by starting over without getting all of them. This is okay and you’ll get another chance at them by going back through the portal stages. It would be best to get them on the first pass as they will help more when trying to get to the higher tier gear on the next run through.
What are legendary artifacts? They are buffs that apply to the whole party and will carry over when choosing the option to prestige. There are 10 bosses and each of them will drop 4 artifacts for a total of 40.
There are also legendary weapons that can be purchased for 200 gems. These weapons are a better buy than the 210 gem tier 20 because it will still be around when your prestige when the tier 20 will reset back to nothing and be deleted. The tier 20 is a waste of gems if your going to purchase it that way. If you have enough gold to buy it then your probably pretty far in the dungeon and need it.
For more info visit the Dunidle Wiki with guide, tips, walkthroughs and more.