You and your parents think about it for a moment. Then, Dad turned to the old man. "I'm interested, but I want to keep my hands." he said.
The old man thought. He motioned for you and mom to move away. Then, pointing at Dad, he mumbled something. Dad felt the changes happening.
First, his clothes disappeared. Then he gained gills on his neck. Then his legs grew huge green scales and instantly turned into a tail.
Dad was now a merman!!!! Or better still... a Mer-Dad!