Shadowfiend
Shadow Word: Death has a 40% chance to summon a Shadowfiend for 5 sec when damaging targets below 20% health. Summons a Shadowfiend to attack your target for 5 sec. Generates 1 Insanity each time the Shadowfiend attacks.
Tree position
In the Discipline Priest talent tree, Shadowfiend sits in the Discipline specialization talents, row 8 of 11. It is a single-point node. Its row opens once 20 points are spent in Discipline Talents.
Connected above
The tree draws a line into Shadowfiend from Abyssal Reverie.
Connected below
Shadowfiend leads on to Death's Torment and Inescapable Torment.
Death's TormentShadow Word: Death deals damage 2 additional times at 15% effectiveness.

Same row
Also on this row: Divine Procession, Inner Focus, Archangel or Mindbender and Shadow Mend.
Divine ProcessionSmite extends the duration of an active Atonement by 2.1 sec.
Inner FocusFlash Heal, Shadow Mend, Power Word: Shield, Penance, and Power Word: Radiance have a 20% increased chance to critically heal.
ArchangelEvangelism increases your healing and absorption effects by 15% for 18 sec.
MindbenderEvangelism summons a Mindbender to attack a nearby target for 12 sec.

Talent trees
Shadowfiend is in the talent tree of 3 specializations. Priest: Discipline (Healer), Holy (Healer), Shadow (DPS).
Shadowfiend Changes by patch
Tracked changes to this talent between game data builds, newest first.
- First tracked in the game data (patch 12.1.0)