This will come naturally through party play plus races & battles both count but, if you are in a rush.
3. Region = Desert
4. Level = The outback
5. Time limit 1 minute
(because you need to win 150 battles anyway, you might as well work on wins too!)
6. Stampedes = None
7. Deadly stampede = Off
8. Add a 2nd controller (guest is fine)*
9. Grab a golden pinata and hit player 2 as many times as you can in 1 minute with the Gwack-a-mole mallet (you are holding very large mallet and player 2 is an avocado). On average i got 1-2 mallets per battle, but often got 4 in 1 minute.
10. Press A to rematch
11. Rinse & repeat
* Wired controllers help but, no problem if not as even if 2nd controller turns off you can still play on.