Tell him about the plan.

"YOU WANT MY MOTHER, POTTER? YOU CAN HAVE HER AFTER I RIP OFF YOUR PENIS!!"

"Dudley, consider this again. You can have your mom, plus it would be me underneath the disguise. Isn't that your fantasy?" enquired Mrs Figg.

Dudley's face which was red turned to pink and instantly shy. "W-Well-l, y-your..um.. your not my mom. Plus we made a wizard promise or what not that I would sleep with my mom first or we would die."

"That's not entirely true, cousin. You can have Mrs Figg as long as she's in Petunia's form. You said that you would take your mom in any form. Well, this is a form."

Dudley was still confused, but you got a better idea to explain.

"Dudley, consider Vanilla and Chocolate ice creams. Both are your favourite types of ice cream and if you mix them together you will get a new amazing flavour. That is what we are aiming for you."

Then it clicks on Dudley like a bulb and immediately agreed to the plan. Through the porch window, you see your Aunt returning back. You take a deep breath and you begin to leave.

Your control over Dudley was gone but not his thoughts. He is extremely excited to have sex with 2 milfs at the same time, he then wonders what if Figg was his fucktoy. You then tune out and have an inkling feeling that Figg may regret this plan. You knock on the door and you walk in.