Riptide Entrancer is a rare Creature — Human Wizard card from Onslaught (ONS), collector number 108. Current market price: $1.44 (foil $10.83), TCGplayer market prices via Scryfall.
Whenever this creature deals combat damage to a player, you may sacrifice it. If you do, gain control of target creature that player controls. (This effect lasts indefinitely.) Morph {U}{U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)