Use an ice spell on the plant
From Create Your Own Story
You use your strongest Ice spell to freeze the plant. The vines holding the knight freeze as well so when you smash them at the base they shatter and he falls to the ground shattering the vines attacking him as well. You blast the rest of the plant with fire and it dies instantly. Donnel goes over to the fallen knight and picks him up. The two of you head back to Donnel's house and Donnel places the still uncontios knight in a bed up stairs with a pair of ragged cloths. Donnel thanks you for saving his land from a killer weed and asked if he can repay you. You smile and say.
Let me take care of the knight