The Thegian Pendant of Stealth helps evade a portion of the enemies on each level. By default, every level (after the first 5) has 100 enemies. At its maximum level of 5 the Thegian Pendant of Stealth will reduce the number of enemies on each level to half of that, or 50 enemies per level.
I personally dug this up in the ruins of Thegius. I'd keep it for myself, but a man's got to eat...
This is a key Artefact to upgrade and max. However, you'll want to get a start on your Headband of Perception and your TAP or DPS Artefact first. Once you're measuring your runs from 1 to 100 in hours instead of days, look to get this Artefact and max it quickly. Cutting the monsters per level in half helps greatly with those really deep runs.
Enemies Evaded = level / 10
Level Cost = level * 10
Artefact Levels Edit
|Artefact Level||Enemies Evaded||Cost (in Crystals)||Cumulative Cost|