In the scene where Atom Ant hits a Dastardly duplicate into the floor, when Atom Ant hits him with the mallet, the bottom half of the duplicate's goatee turns white.
In the scene where J. Dastardly makes a human train with his duplicates, there are a total of 12. That's 3 too many.
In the scene where the Dastardly duplicates come in and all the loot is on the table, there is one extra Dastardly.
J. Dasterdly Deeds: Stop this if you can.
(J. Dastardly fires a cannon ball at Atom Ant)
Atom Ant: Anything to oblige. (knocks cannon ball back into the cannon and it flies outside with J. Dastardly)
Atom Ant: Had enough?
J. Dasterdly Deeds: Let's give him the old locomotive charge.
Atom Ant: I had better derail this choo choo.
Atom Ant: It must have been a case of mistaken identity.
J. Dasterdly Deeds: Of course. I'd have to be a cat with nine lives to be in all those places.
Atom Ant: I wonder if J. D. could be up to one of his old tricks.
Atom Ant: I feel so up-and-at-'em good, I could lift a mountain.