My best experience as a player was playing the scenario of Alien (the movie) in a setting without alien... surprising, until we found the eggs (and it clicked ) and we all died soon after.. My guess: it work with any horror movie transposed into any normal setting. As a GM the most fun I saw my player have, is letting them save the life of a godlike figure (Elric of Melnibonée in the game of the same name) when they were newbs with 2 adventure on their belt. And they wielded the most powerful (and dangerous ) weapon of the world for a few round of combat.. it make their day... until it corrupted one of them It worked.. because Elric is nothing without his weapon, I dont see it happening with Elminster. Have good fun in your new city
It's just a retell of the alien movie story. No scenario to create: An alien is attacking (the one from the movie) and laying eggs. Period. You dont even have to gave it proper characteristics, it's just about scaring the players with an evasive powerful unexpected foe striking and disappearing in a heartbeat.