This sort of sounds like an oath the twins would have made once they decided they were going to cause mayhem and mischief.
Well, as you can see I am Kita Kudai, not J.K. Rowling, so I don't own Harry Potter in any way, shape or form.
Innate jokesters fear no punishment
So take to some mischief.
Open your arms.
Let devilish delight
May your arsenal of
Naught Pranks and skillful
Lies ad you in dodging trouble
Yet you cannot deny the thrill you feel inside
Swear to cause mayhem, mischief and chaos
While fighting to keep your nose clean.
Extend your ears,
And listen to us – the
I'm under the impression
My brother and I are
Under appreciated in our fine art.
To never know the joy
Of getting caught but
Gone are the times
Of complete and utter
Don't live a life controlled by others.
I Solemnly Swear I am up to no Good