"This cat is a bad cat."
Translation:Ten kot jest złym kotem.
Hovering text shows possible translations, but they are dependent on the context. It could be translated as "to" if the sentence was like "This is a bad cat", where 'this' is in fact the subject of the sentence, and 'to' would be the only option.
But in the sentence discussed, 'this' serves as a demonstrative pronoun, and has to match the gender of what it describes - the cat, which is masculine, thus 'ten' is the only option.