All levels completed:

Press Up, A(3), Down at the title screen.

 

Fifty lives:

Press B, Up, B, Select, Y at the title screen.

 

High jump:

Press Up, Y(3), Down at the title screen.

 

Invincibility:

Press X, A, B, Y, Up, Down at the title screen.

 

Ninety-nine diving suits:

Press B, Left, Up, B at the title screen.

 

Ninety-nine Nerf balls:

Press B, A, Left(2) at the title screen.

 

Ninety-nine portable holes:

Press Right, Up, Select(2) at the title screen.

 

Ninety-nine smart bombs:

Press X(2), Up, Down, X at the title screen.

 

Rubber floors in medieval levels:

Press B, A, B, Y at the title screen.