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