Jitsu Squad - Outstanding Combo Trophy Guide
Odds are you'll earn this playing as Baby naturally, but for anyone worried about it or having trouble getting it, I included two methods. I think the Baby one is easier to do, though if you get the gun with Aros you could literally shoot enemies (has about 100 bullets), and then just push circle to hit 250.
0:00 Baby Method
1:14 Aros method