"Beth wyt ti'n feddwl o Dewi Lingo?"
Translation:What do you think of Dewi Lingo?
Actually the mutation is correct here. In 'fancy' Welsh it would be "Beth wyt ti'n ei feddwl o Dewi Lingo?" i.e the masculine "ei" causes a soft mutation. Even though the possessive pronoun is often left out the mutation still remains.