If you want to earn 30,000 bonus points, make sure you end a level with eleven times more shurikens than the number of lives you have left.
Defeating Neo Zeed
As you already know it is almost impossible to get through the maze. For those of which who have a stash of jujitsu & power ups, save these untill Neo Zeed. As soon as you start to fight,use lightning jujitsu, and crouch next to him and fire at will. As soon as the sheild is gone, use it again, and reapeat, Zeed is dead in 5 seconds.
Extra Life
On the first level, enter the second building and find 2 spikes near each other. Use the "ninjitsu of mikin". An extra life will appear between the spikes.
Special Bonus
Finish any level with enough shurikens to equal 11 times the number of lives remaining, and you will receive 30,000 bonus points (i.e., if you have 7 lives left, finish the round with exactly 77 shurikens.)
Unlimited Knives
At The very beginning of the game go to the options menu and change the number of weapons to 00, then do not do ANYTHING for ten seconds, then the 00 will become an infinity sign and your weapons will never run out.
Unlimited Men
In round 4-2, there are many power-ups hidden that are revealed only by shooting them. On the first platform, jump and shoot and you'll reveal a 2-up on the platform across your position. Get it, die, and repeat! There's another 2-up on level 3-2. Go to the second elevator and locate the crates that are in the middle of the screen (on the second level). Then shoot the bottom-left crate until the 2-up appears.
Unlimited Shurikens
For unlimited shurikens, set the number of shurikens on the Options screen to 0 and wait about 20 seconds. The zero will turn into an infinity symbol, giving you an unlimited number of shurikens.
30,000 Bonus Points...