A suggestion for a change for flames of oblivion since the ability feels kinda meh overall.
It lasts for 15 seconds and launches a fireball every 5 seconds, its just boring really.
My suggestion would be to firstly remove the floating fireball(because ugly) but keeping the flames on the character and change the damage to a damage over time "aura" for 15 seconds since DK's are about the DoT skills.
The animation should also be changed to something more explosive. I always thought the mass hysteria cast animation would be fitting for flames of oblivion as you burst into flames.
Flames of Oblivion - Burst into flames causing X damage instantly to enemies around you and an additional X damage over 15 seconds.