Learn German: Der kaputte Mixer hat mir den Teig ruiniert. - The broken mixer ruined the dough for me.

The pronoun mir acts as the dative of disadvantage (Dativus incommodi). It shows who is negatively affected by the action—in this case, whose dough was ruined. While you could technically say für mich, using the dative pronoun is much more natural and idiomatic in German to express that something went wrong "on me" or to my detriment.

Wait, why doesn't the past participle of ruinieren have a ge- prefix?

Verbs that end in -ieren (which are usually loan words, like studieren, passieren, or ruinieren) do not take the ge- prefix in their past participle. They simply take a -t ending, making it ruiniert.

Since Mixer is masculine, why is the adjective kaputte instead of kaputter?

Because it follows the definite article der. When a definite article already clearly shows the gender and case (nominative masculine), the adjective uses "weak declension" and just takes an -e ending. You would only use kaputter if the article didn't show the gender, like in ein kaputter Mixer.

Could I change the word order and say hat den Teig mir ruiniert?