When you fight the clown and Roo, defeat the clown first and Roo should hop away off the screen. When you lose all your lives and continue, cycle through the characters and Roo will now be available.
Ending 1
To get Ending 1, successfully rescue the Chief in Stage 6 before his health runs out. Then, at the end of Stage 7, defeat Robot Y before the time limit runs out. You will see the true ending.
Ending 2
To see Ending 2, manage to rescue the Chief before his health runs out in Stage 6. Then, in Stage 7, defeat Robot Y but let the time limit run out. You will see Ending 2.
Ending 3
To see Ending 3, let the Chief's health run out in Stage 6. When you go to Stage 7, you will see that it is changed. Make it to the last boss and defeat him. You will see Ending 3.
Ending 4
To see Ending 4 , simply set the difficulty on Easy Level and beat Robot X in Stage 5.
Extra Lives Select
Go to the options screen and select the ''Lives'' option. Press and hold UP + (A) + (B) + (C) on Controller 2, and press LEFT or RIGHT on Controller 1 to select the number of lives you can start the game with. You will now be able to select 9 lives, past the default max of 5.
Get Roo
At the title screen, hold Up and B, then press Start. A kangaroo named Roo will now be available at the character select screen.
Get Shiva
After beating Shiva in the first stage when you get the last hit, press B+Start and hold it. When the continue screen comes up you'll be able to play as Shiva.
Play as Ash
To select Ash, defeat him, then hold A on Controller 1. After losing all of your lives, you select to continue and you can choose Ash as your character.
Play as the same character
Hold Down+C on controller 2 as you enter 2 PLAYER mode with controller 1.
Another way to get Roo...