Shadowy Spikes delays the scream of a spiked enemy, giving Evie a moment before the area reacts. It is earned in the Jack the Ripper expansion.
Shadowy Spikes unlocks after this challenge: impale an enemy from cover or from an air assassination opportunity, 20 times. Shadowy Spikes is one of five perks added by the Jack the Ripper expansion, all earned as Evie in 1888.