Seawinkle is one of the 3 main Sea Ponies from My Little Pony: Rescue at Midnight Castle.
She is first introduced in the scene where She and her friends Wavedancer and Sealight. She helps the other seaponies save Megan and Applejack from the sea. She and the other seaponies are able to keep Applejack and Megan in the bubble while Singing and Showing them that they can help if the ponies needed them again.
They later re-appear when Megan threw a Seashell that Sealight gave to her if they needed them. Seawinkle knew that Touching the Gargoyle's face would open the gate.
Just like her friends, Sealight and Wavedancer, she gets her design from Bowtie. A pony on land.