Feb 1 (Reuters) - Activist investor Barington Capital has set its sights on Mattel and is seeking big changes to boost the toymaker's stock, the Wall Street Journal reported on Thursday.

Barington Capital has built an undisclosed stake in Mattel, according to a letter sent to CEO Ynon Kreiz, the report said, citing a letter seen by the Journal. (Reporting by Gursimran Kaur in Bengaluru; Editing by Arun Koyyur)