In Area 5-3, there's a 1UP on the 3rd floor of the tower. Then, go back down the ladder to the 2nd floor, and then back up to the 3rd floor. The 1UP will have returned. You can do this as many times as you want.
Mid-air sword glitch
Normally, you can only slash once or twice slowly with your sword during a jump. With this glitch, you can rapidly swing your sword multiple times in mid-air. To perform the glitch, jump in the air, hold 'down' on the d-pad while in the air, then swing your sword with 'B'. While still in the air, release the down button, then immediately hold the down button once more and attack again. You will swing your sword more rapidly than normal. You can repeat the process until you land. With enough practice, you can swing your sword up to 4 times in the air. This will only work while you're in the air. The glitch works very well with slow-moving or stationary bosses, allowing you to get in a few extra hits.
Sound Test
When the screen says Techmo Presents 1989 hold A, B, Left, Down, Select, and press Start.