The Return of Hydro-Man: Part 1 - S5-E7
Continuity mistake: When Spider-Man is in the lab analyzing Mary Jane's jacket for clues, the inside of the door to to the lab has the door knob on the right side. When Debra Whitman is trying to get in the lab, the door knob on the outside of the door is on the right side as well, when it should be on the left side. The inside knob also disappears when the security guards break the door down.
And the Sea Shall Give Up Its Dead - S1-E1
Other mistake: When Tony Stark is typing on the keyboard, some of the keys are depressing without him touching them.
The Origin of the Fantastic Four: Part 1 - S1-E1
Continuity mistake: When Sue is holding up the book for Dick Clark, her right hand is on the bottom of the book on the spine side, and her left hand is in the upper right corner. When the shot changes, her right hand is suddenly closer to the top-left corner. (00:02:18)