An idea I have is Abby is at the beach with her mom while her dad and bozzly are watching the hotel. while at the beach Abby spots a multicolored narwhal out in the middle of the ocean, then once Abby gets near the water she tries to do a whale call which gets the narwhal's attention eventually making his way towards Abby. once the Narwhal arrives at the shore Abby calls her mom over. as Abby goes to pet the narwhal his tusk glows them emits a ball of light turning Abby and her mom into mermaids. they would hitch a ride on the narwhal to the bottom of the ocean, then spot a baby narwhal who appears to be stuck in a shipwreck. Abby and her mom would work together to free the baby narwhal and they spent the rest of the day as mermaids under the sea. When Abby goes to use her whale call, real whale noises are heard and the narwhal comes to her calling, then when Abby tries to tell the narwhal to take them back to shore she would end up only able to speak whale as it turns out she's slowly turning into a narwhal. Abby and her mom make back to the shore in time before Abby could become a full fledged narwhal and are back to their old selves and head back.