The Caparison of Lament is a unique horse saddle in The Witcher 3: Wild Hunt added by the Hearts of Stone expansion. You are given this saddle if you allow Master Mirror to take Olgierd's soul, and you choose the first option: "To be as swift as the wind". Equipping it transforms Roach into a demonic-looking black horse with glowing eyes. According to the description, it also applies a short-range effect, possibly similar to the stagger caused by the Axii ability Delusion. Be aware of the fact that in some cases (known on PS4) it will only be the left eye of Roach that is glowing - not both of them.