To obtain this trophy, set the Versus Match options to Team Battle and put 3 opponents on the opposing team and you set yourself to fly solo.
Set the match parameters to whatever you are comfortable with to ensure that you win. I set mine to Team Battle with High AP Accumulation setting and a 3:00 minute time limit.
The easiest way to get AP quick and to achieve 2 and 3 Supers (to score multikills) is to choose a character who deals high combos. The obvious choices are Kratos, Dante and Raiden for me.
I won this trophy with Dante against Toro, Fat Princess and Spike on the Time Machine stage.