Describe the bug
These are Zekvir minibosses that spawn on tier 9 delves and higher.
Wowhead article on them

Anub'vir - Impaling Spikes (449038) - dodge brown swirlies on ground
Transcript: Kriegval's Rest, Dagran's Day Out.zip

Venombite - Evasive Dance (458325) - channeled ability that can be stopped with stuns, cannot be interrupted. Don't think it recasts after being stopped?
Transcript: Underkeep, Torture Victims.zip

Tala and Velo
Venom Volley (458104)
Grasping Darkness (458099)
Both are AOE abilities that can be interrupted. Grasping Darkness does ~3M damage to everyone, and Venom Volley does double that over 12 seconds, but can be removed with poison dispels.
Transcript: Nightfall Sanctum, Dark Rituals.zip

Screenshots
None at the moment, but can obtain them if necessary.

Which version of DeadlyBossMods are you using?
Dungeons r173-1 alpha