What's wrong with the abilities chosen already? Vampiric Aura would allow the Death Night and melee allies to gain health when attacking opponents, meaning that they last longer. When you've got a buff on a hero, it always increases the performance of your units, not decreases the enemy's performance. Perhaps that Fear ability (name would have to be changed) could be put in a ward for the Sorceror. That'd actually be kind of cool.
And Misha, the Death Knight is a Strength Hero. Their function determines how they are used and the spells they get. Agility Heros are built to disrupt enemies, but slaughter. That would go for the Blade Master, the Warden, the Dread Lord, and the Mountain King.
And what would you want in your fever defuff? If we add too many auras, the balance will be broken and the Naga will most definetly be on top, no matter how you played. I think we're fine with the biffs that we have.