Hold these buttons at beginning of each stage to activate the weapon:

Stage Weapon 1P side 2P side
1 Shotgun down A
2 Shotgun A B
3 Laser upright+A+B down+B
4 Shotgun downleft+B leftup
5 3way A up
6 Auto left right+B
7 Shell upleft down
8 3way left+A+B A+B
9 Laser downright+A+B rightdown+A+B
10 Shell upright+B downright
11 Auto upleft right+A
12 3way right+A+B rightup+A
13 Auto up down
14 Laser upleft+A+B right+A+B
15 Shell downright+A left
16 Auto right+A left