There are currently only two WD class quests at 15 and 25, just like other classes.
Level 15 - Bone Chant power Level 25- Mournsong power
Bone Chant is the power Old Scratch starts with, that summons a skeletal Corsair minion.
Mournsong is the third spell in the "Ghostwail" line of powers (Ghostwail -> Soulreaver -> Mournsong). It deals damage up front and leaves a damage over time debuff on the target. It has unlimited range just like Ghostwail and Soulreaver.