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: I believe it was just a way to try and show the suit is "oily" or reflective. It also helps define the character's features since otherwise, he'd just be a flat black color. It's similar to how the black suit Spidey had blue outlines. (I don't know why they chose a pink/red color... maybe because red is associated with power/fire/war, so it's a more "evil" color?)
TedStixon