Nimue smiled a bit and nodded. It was hard to think her alter-ego was pure evil. But at least Merlin could see the difference. "You're so young," she observed quietly, addressing no one in particular.
When he mentioned the spell, she smiled. "Me, teaching you magic?" She chuckled. "It really is a different world, isn't it?" She reached behind her neck, unfastening a crystal necklace she wore there. She pulled the jewelry off and ran her fingertip over a sharper edge, drawing blood. "It is an attunement spell. In the case we were separated, we could find each other. It only works with you." She rubbed a drop of blood over the leather cord that wrapped around the crystal. It was dark enough that the blood didn't show. She said a few words and the crystal flashed. Then she handed it to Merlin. "Concentrate on that if you need me."