Go to the training mode, and choose 3 CPU.Take characters with the triple kill with a level attack 1 is possible (Radec, Kratos, Dante..)
Boost your points until the first level, try to align your CPU and launch your attack when they are aligned.
Kill the three CPU all at once and the trophy fall.
You can make this trophy in all the modes but we're going to say that this way will be the easiest to realize this trophy.
You should unlock the trophy "Three for One"
Video (credit to