At 3rd, 6th, and 9th level, Fellblades get to choose a curse to improve, from the following list:
Baleful Geas
Baleful Polymorph
Curse of Despair
Dread Seizure
Hideous Blow
Geas
Type of Feat: Class
Prerequisite: Fellblade Level 3+
Specifics: The Fellblade's Baleful Geas Invocation (should they have it) becomes more potent. The target gains additional +2 strength, instead of having a strength damage, while the duration of the invocation becomes double, 2 minutes / caster level.
Use: Automatic
Baleful Polymorph
Type of Feat: Class
Prerequisite: Fellblade Level 3+
Specifics: The Fellblade's Baleful Polymorph Invocation (should they have it) becomes more potent. The duration of the curse increases to Caster Level * 2 minutes.
Use: Automatic
Curse of Despair
Type of Feat: Class
Prerequisite: Fellblade Level 3+
Specifics: The Fellblade's Curse of Despair Invocation (should they have it) becomes more potent. The target's ability scores will decrease by 4 instead of 3 on a failed save, and now lasts 4 rounds.
Use: Automatic
Dread Seizure
Type of Feat: Class
Prerequisite: Fellblade Level 3+
Specifics: The Fellblade's Dread Seizure Invocation (should they have it) becomes more potent. The target's attack bonus will decrease by 4 instead of 3. (Only player characters make a save.)
Use: Automatic
Hideous Blow
Type of Feat: Class
Prerequisite: Fellblade Level 3+
Specifics: The Fellblade's Hideous Blow becomes vampiric. A successful hideous blow hit will vampirically heal the fellblade a number of hit points up to the Fellblade's current class level.
Use: Automatic