When Meredith is mobbed by the dying roses in the garden in the Unseelie mound just outside the throne room, Doyle ordered Sithney to give him a sword. Sithney started to obey despite Cel's order for his people to keep thier swords, but the doors were covered in thorns before he could give the sword to Frost who was reaching for it.
Doyle selected Sithney and Nicca from the crowd in the aftermath and sent them summon Kurag, the goblin king, when Meredith was injured by the roses, since she was all ready bleeding, she thought to use it more constructively than letting it soak into bandages.
Note: His description says he had long brown hair, but in the same sentence, Nicca was described as having dark purple hair and pale lilac skin. Since it was later confirmed repeatedly that it was Nicca who had long brown hair, it is probable that the descriptions in this case were simply reversed and it was Sithney whose coloring is shades of purple.