Having already surprised everyone once by appearing in the form of a badger, Merlin did it again when he transformed into human form. 

He shocked the four of them even more when he calmly announced that the only way King Offalmire, who was trying to steal the special supernatural ‘Thirteen Treasures of Britain’, could be destroyed, was with a special arrow dipped in a magical poison.

Merlin then handed Sylvia, the twins mother, a small parchment tied with  black ribbon.

'Guard this parchment well, lest it fall into the wrong hands, as it lists all the ingredients needed to make the poison. Some of your tasks will be difficult, even treacherous. But you need every one!’