Template:Tooltip Debuff Shadow Flame is an ability that Nefarian, Ebonroc, Flamegor, and Firemaw can cast. It deals about 3938-5062 cone-shaped shadow damage and is not partially resistable.
Furthermore, it has a Damage over Time effect on its target for 1750-2250 damage per second for 10 seconds [1] unless the recipient is wearing an 
[Onyxia Scale Cloak].
Notes
When Nefarian lands at the start of Phase 2 of his encounter he will use an AoE Shadowflame that ignores LoS, this version of the spell only does about 1000 shadow damage, but still applies the fatal DoT if an [Onyxia Scale Cloak] is not equipped.