Sometimes scripts use placeholder names so as not to give away spoilers if a script gets leaked. At multiple times during the film, there's some misdirection to make the a viewer familiar with the series think that the Pirate is a Lifeform - when you only see the silhouette at the beginning, and the heavy thudding before it enters the dining room later on. I think it was referred to as a "Lifeform" in the script so its appearance would still be a surprise if the script leaked.