Dragon Ball: Raging Blast 2

This isn't so much of a solution but if you want this quick & easy wait until you have some of the ability down items e.g. Super Health Power Down & Defense Power Down & then start equipping the CPU you'll be fighting with all Ability Down Items

I got this achievement in around 10mins with a load of power down items equipped to the CPU & just went to fight again to speed things up. Hope this helps someone

The method i used to beat the CPU 50 times and get this achievement really quickly was this :
Firstly, pick Legendary Super Saiyen 3 Broly, Equip him with the High Tension Start, and put on Super Attack Power Up S, M and L.
Next pick Videl as your opponent and equip her with the items Super Health Power Down and Defense Power Down.
Now go ahead and start a Versus match against the CPU using both your customs characters.
Once the match begins, hit up on your RS and Legendary SSJ3 Broly should hit her with Double Eraser Cannon (i think thats what its called) and it will kill her within 2 seconds of the match starting, now all you have to do now is hit Rematch 49 more times and "Achievement Unlocked".
Hope this helps you guys out.
Should take no longer than 10-15 minutes to do the full 50 matches.