Bakugan: Defenders of the Core

Go to Battle arena from the main menu and choose Duel.
First change the settings to 1 round instead of 3 so the matches goes faster. Then pick your Bakugan that you like and put your Bakugan up to 3 health stars and your opponents to 1 because it will make it much easier and faster to kill your opponent.

Now all you have to do is to win 30 times against the CPU and the achievements will unlock :)

*Credit goes to Sakura460 from x360a*

From the main menu select Battle Arena, then select Duel. Go into the Battle Options and change the CPU level to easy and rounds to 1. Then select P1 VS CPU. You can choose whatever Bakugan you like but put your opponent as one who is weak to yours. I used Maxus Dragonoid against Hades. Put your health to 150% when you're selecting your character with and put your opponent's health to 50% with when selecting it. The arena Interspace is the smallest so I suggest that.

Once the match starts you can do a physical combo such as then just spam , don't hold it down as you'll most likely miss. Matches should take about 20-30 seconds each. Just retry at the end and repeat until you have 30 wins.