Doof's opinion on PerryEdit
Doofenshmirtz does not like Perry the Platypus; he traps him and then they fight, but sometimes, he shares fun things with him. In one episode, as mentioned earlier, he once went shopping with him, more specifically, in the episode "Unfair Science Fair Redux (Another Story)"
Although Perry is his nemesis, in the episode "Road to Danville" and the episode "Oh, There You Are, Perry" the two work together, but they are still enemies. Ah, more like frenemies.
Perry's opinion on DoofEdit
Perry has the same opinion of Doof as Doof has on Perry as Perry has on Doof as he has on him. Etc.