Clue 13 (fequently known as 666) is a clue discovered by Bettany in S2E3 "The Future Of The Wickford Gang".  It was a hidden message that Darcy wrote down in Bettany's Academy portrait to help find a Dissapearance Laser.

It said:

"Live A Series Excluding Ravens"

"Bystand 3"

"Figure It Relaxed Standing There"

"Rebel Or Worry"

"Don't Assist Reality Cruelly: Yield"

Starting at each first letter it spells out "Laser B3. First Row.'- Darcy". 'It is named "Clue 13" because of the laser number "L13". This was then used to disappear all of the zombie sent out by Angelina Zombielestrange.