This is written by the great Roger Stern and illustrated by Bruce Timm–a great creator best known for his animated on Batman. Let’s start with the cover. “You’ll gasp at the identity of our mystery villain!”
This is a tongue-in-cheek Silver Age tale that takes place between Avengers #1 and #2.
Not sure if it’s even canon. But it’s such a refreshing break from many of the super-serious books that came out in 1999.