Undaunted Infiltrator is a medium armor set. When you use an ability that costs Magicka, your Light Attacks deal an additional 774 damage and Heavy Attacks deal an additional 1161 damage for 10 seconds.
A mirror version of this set (Undaunted Unweaver) drops in Blackheart Haven.
The Undaunted Infiltrator set is part of the base game. It drops in Arx Corinium in Shadowfen. Each set item is bound on pickup. You can acquire medium armor, weapons and jewelry of this set in the Breton motif style.