https://www.youtube.com/watch?v=RYLpQFuxV5Y
Not technically a monologue per se, but this would be the one I'd use.
RT @TheReelAnderson@twitter.com
Aliens arrive on earth with the intent of wiping out the entire human race. The fate of the world depends on a monologue from ONE actor.
Who are you picking?
🐦🔗: https://twitter.com/TheReelAnderson/status/1257870388614164481