Lamia's Song is a light armor set. When you use an Ultimate ability, you heal yourself and your allies within 20 meters of you for 30 Health per point of the Ultimate's cost.
(Note: For a 250-point Ultimate like Warhorn, this means the entire group will be healed for 7500 every time you use that ability)
The Lamia's Song set is part of the base game. It drops in Arx Corinium in Shadowfen. Each set item is bound on pickup. You can acquire light armor, weapons and jewelry of this set in the High Elf motif style.