Here is the full list of all 15 Willy-Nilly Knight achievements.
Finish one of the love story lines
Go through the whole game and find out the final of the story
Find the unique Excalibur sword
To present Idril with something very important
Find out who is Arthur's true enemy and the root of all evil
Visit all the locations on the World Map
Destroy all the bosses in the Castoff Dungeon
Gather the team of all 4 characters
Help the little girl to go back home
Fuel up Bob's still
Kill the boss in a Spiders Crypt
Kill the wolf leader
Fall in love with Guinevere
Complete first Siegfried's task