OH SHIT. T-1000 mosquite, with a built in syringe full of the nastiest, most contagious disease we can produce or steal. Release them into major cities. Inject people with the disease. When the syringe is empty, return to a safehouse (a home or apartment we've bought, one of many across the world), where there's a small stockpile of the virus. Refill the syringe, fly back out and infect another. If attacks like this are carried out simultaneously, within a week, the world could be facing a serious epidemic. NYC, LA, Seattle, Chicago, Miami, Atlanta, London, Paris, Moscow, Madrid, Bangkok, Hong Kong, Mexico City, Perth, Lisbon, Stockholm, Berlin, Munich, Rio De Janero, Singapore, Tokyo. Major port cities, major traffic hubs. Hitting airports.
Shit would be devastating.