These wings gives the Double Jump mod, and a new death effect, a dark black swirling vortex not unlike those seen around Growganoth. It is also the same effect when a player respawns/dies while wearing a Cape of Shadows (black swirl replaces the growtopian). There are tiny violet sparkles when you jump too. It looks like Devil Wings but purple in colour.
This is a unique sacrifice, so dropping a stack will yield an equal amount in return.