I'll hire super-scientists to create horrible grotesque monsters and unleash them into the streets/sewers/back alleys. In the ensuing rash of grisly murders, the population will be frightened. Eventually, the government will declare martial law, and citizens will be trapped in the city won't be able to leave their homes at night. While the the military is busy trying to exterminate the monsters, I'll use the subsequent economic depression this has caused to seize control of local businesses and infrastructure, while providing relief to the beleaguered citizens, making them love me. I'll then use my know massive influence to install a puppet government. I'd then trigger the kill switch in the monsters, which will allow the military to withdraw, leaving me the effective ruler of the city.
If I ever get bored and wish to destroy the city, I'll instigate a massive brainwashing program through subliminal messaging that will cause everyone who sees it to become violent savages who attack everyone on sight. The city falls to ruin in the ensuing carnage, and I safely escape to another location with all their money.