Free Play
Press X and Y at the same time at the title screen, then press START to get Free Play.

Raccoon Bonus
Instead of randomly shooting down bonus characters, concentrate on Raccoons instead. Consecutive shots at the Raccoons will let you achieve a much higher score.

Score Coefficients
Wondering about how to get the highest possible scores? Sammy's got the answer:
Numbers displayed in the upper part of the screen, such as "x1.17" underneath "Experience," signify the increase of points you score when you hit an enemy. When this amount is high, you earn increased points for hitting an enemy. Elements affected by this score are: the number of shots possible, remaining life (activates Crazy Mode with 1 remaining life or less), the number of players, the condition of the machine gun charge, "GAME DIFFICULTY" and "START LIFE."

Getting shot on purpose and reducing your remaining lives to 1 or less lets you enter Crazy Mode. In this mode, your score for hits increases dramatically.

When the level in the Game Difficulty option is high, or if the number of lives is low per credit in Start Life option, you can obtain a higher score. It is best to keep an eye on the Score Coefficients (upper left screen) to adjust these settings