Unsettled Mariner is a rare Creature — Shapeshifter card from The List (PLST), collector number MH1-216. Current market price: $5.10, TCGplayer market prices via Scryfall.
Changeling (This card is every creature type.) Whenever you or a permanent you control becomes the target of a spell or ability an opponent controls, counter that spell or ability unless its controller pays {1}.