Sins of the Fathers Chapter 1: Doctor Strange - S3-E1
Revealing mistake: When Mary Jane and the other servants of Baron Mordo are flying through the city, they literally disappear into thin air. Probably a problem with rendering the 2D animation within the 3D animation. (00:01:00)
Sins of the Fathers Chapter 1: Doctor Strange - S3-E1
Revealing mistake: The same shot of debris falling from the ceiling in Baron Mordo's lair is used twice. (00:14:25 - 00:15:45)
Sins of the Fathers Chapter 7: The Man Without Fear - S3-E7
Revealing mistake: During the fight with Kingpin recycled footage is used from Season 1 Episode 7 Doctor Octopus: Armed and Dangerous. It's obvious when you see the background looking like the warehouse along with Doc Ock's machine behind Spider-Man.
Sins of the Fathers Chapter 13: Goblin Wars - S3-E13
Revealing mistake: Several shots of the Green Goblin are recycled from the earlier episode "Enter the Green Goblin," with some of them being used multiple times in this episode.
Answer: Yes. Many things that would have been in the sixth season would have had Norman Osborne returning from limbo and reclaiming the title of the Green Goblin, Richard Fisk, the son of "The Kingpin" Wilson Fisk would return as a crime lord known as "The Rose", Ghost Rider would have appeared to help Spider-Man stop Dormammu from returning to Earth and Madame Web and Spider-Man would rescue Mary Jane from limbo.