Spell: Mark of Shadow removed by suffering from Mind Flay
npc=16469 uses two spells, Mark of Shadow (31394) which is a 2min debuff which increases shadow damage received, and Mind Flay.
However, as soon as they cast Mind Flay on the player, this debuff gets removed.
Additionally, they will always fail their first Mind Flay, as well as any other Mind Flay later on, unless you are static. If you move they will always cast and immediately fail the Mind Flay spell. Presumably due to the missing COMBAT_MOVE flag, or something else?