A concealed blade the empress uses to keep herself perpetually wounded, blocking Carl's ability to mark her.
Carl notices early that Empress D'Nadia has a health bar showing a very slight injury that can't be his doing — Tech Shield hits cost no health — and that she is somehow keeping herself from healing completely. He realizes she's doing it on purpose to lock out the Ring of Divine Suffering, which only works on a target at 100% health.
The mechanism surfaces when a knife clatters to the floor mid-mauling. She reaches for it, but a clockwork Mongo snaps the tentacle holding it clean off and the knife skitters across the room. With her self-injury tool gone, Carl casts a Heal Scroll and marks her; she resorts to biting her own hand, but too late.
A small concealed blade carried among her tentacles beneath the gown.
D'Nadia's countermeasure against being marked, defeated when her tentacle is severed.