Is a reward from the event dark blessing after u get all blessings u gain glith cause one of u monsters gain str, spd and int per second but lose even more hp per second until die.
getting all 4 deals then taking the dark glyph does do that. It creates a mark on the ground that hurts and monster that stands on it but increases all damage they deal. (The damage it deals and bonus it gives both increase the longer the battle goes on too)
