When Papi, Chloe, their puppies, and their owners first come into the hotel, Oscar welcomes them with open arms. He tells Papi that the puppies would do fine in the hotel school for dogs. He is also seen talking to Chloe a few times.
However, at the garden, Papi begins to grow suspicious on what is going on behind the gate. Oscar stops him from doing so. Oscar himself is seen going there a few times and Papi later learns that it involves Jenny and Mr. Montague. Other than that, he is pretty much never shown any real acts of villainy, despite being one. Later, Oscar witnesses Jenny's defeat as she was exposed by Papi. In the end, he is taken to a police car by Delgado and headed to prison (most likely the pound).
It is unknown why Oscar was involved in Jenny's scheme, though it could have been because he was loyal to her, or was probably forced into it.