I have actually been waiting for this, because I want to put my rough script for a different take on the album here. I always felt that Uderzo let his dislike of manga override the creation of an actual Asterix story here, so I would try to make i slightly more like earlier albums while still retaining the whole manga and american comics theme.
The story begins in Rome, where the city, sleeping in the night, is menaced by mysterious alien who came from a grimacing cylinder in the sky. A mysterious entity (covered in shadows) has cornered Ceasar and beaten his bodyguards. Ceasars asks what the figure wants, and it answers that it has come to test it's skills against the denizens of earth, for it wants to become THE STRONGEST. Ceasar, being a shrewd politician he is, quickly gets out of trouble by admitting that he is not THE STRONGEST, for a mere village of gauls has beaten him on multiple occasions. Next pages shadowy figure leaves for his cylinder and flies away in the night, the afterburn demolishing a hapless pirate vessel on the way. Maybe have a short pun about the supposed UFOs in medieval art.