Serpent-Coil Braid is an epic trinket for mages.
The effective +damage from this trinket is difficult to calculate, as it is not always prudent to use Mana Gems the moment they come off cooldown. Assuming one does however, this item adds an additional
225 * (15 / 120) = 28.125 +damage
It is important to note however, that the real benefit of this trinket comes from the additional ~600 mana gained from using a Mana Emerald - which can add quite a substantial amount of DPS for an Arcane Mage who utilises heavy Arcane Blast spam.
- Patch 2.1.0 (2007-05-22): The bonus spell damage from this trinket is now removed if the trinket is unequipped.
- Patch 2.0.3 (2007-01-09): Added.