Beefcake is stabbed during a fight about an hour and twenty minutes into the film. We don’t see the stabbing, only his body lying still on the ground before he is buried in the ground (you can see his paw under the blanket he is wrapped in).
One of the characters (Dog) could be described as autistic but the screenplay doesn’t mention this specifically. Mirales is very unkind to Dog and criticises almost everything he does down to how he eats his food and the things he says.