Is there a word for a car that always breaks down and may need to be replaced?. It should be an adjective or a noun

Is there any word for that? Example sentence: "There's nothing wrong with my mood!" Mary cupped her mouth as soon as the __ left her mouth. "Sorry, I didn't mean to shout."

A word to describe a person who is very calculative, presented to be helpful and sharing and knows everything and become the best guy that can lead the team in front of everyone esp. management. However behind the scene, he or she likes to ask knowledge from colleague about certain thing and then...

Which one do I use? Should I, every time I use this kind of conditional, use "were"?

I am looking for a word or a phrase that would refer to the person / agent / entity (not-necessarily human) who controls and can arbitrarily manipulate a computer simulation. Example sentences: "If Nick Bostrom's simulation hypothesis is correct, the _____ could make simulation changes, which...