I figure the only thing that will set Merlin free (assuming he really is in there) is the dagger. Arthurs wants the dagger. If they had gotten the toadstool, theyd have been able to spek to merlin and he’d tell them Arthur trapped him in the tree or something and Arthur doesn’t want that. What he wants is the dagger to be used to he can steal it and not actually release merlin. He went on the trip to ensure the toadstool doesn’t arrive to Camelot.
"I could have the giant duck as my steed!" --Daniel Radcliffe
Keeper Of Tamara's Taser , Jafar's Staff, Kitsis’s Glasses , Ariel’s Tail, Dopey's Hat , Peter Pan’s Shadow, Outfit, & Pied Cloak,Red Queen's Castle, White Rabbit's Power To World Hop, Zelena's BroomStick, & ALL MAGIC