Unlock Alien Zoo Keeper Mini-Game:
Click ALL the lines that have the letter 'O' in them when you view the credits, you will hear a sound to confirma a correct click. Repeat this process when the name list ends and another list eventually appears. When the word 'Secrets' appears on screen click it to play the Alien Zoo Keeper mini-game.
If you complete the game on the 'Normal' difficulty setting you will unlock 'Typ 'o' Shooter' mode and the 'Hardcore' difficulty setting.
Unlock Puzzle Mini-Game:
Select the 'Credits' option at the 'Extras' menu and then scroll to the bottom of the screen where you will be able to see something is hidden. If you now press Y(3), X(3), Y the Puzzle mini-game will become unlocked.
Unlock Bubble Gun:
The Bubble gun will become unlocked if you start a game and do not shoot or take any damage from the aliens for approximately the first 2 minutes.