Go to the ant hill from the main screen. Then, hold C-Up + C-Down + C-Left + C-Right + Z and press R. An arrow will appear at the bottom of the screen to confirm correct code entry.
Return to training level and find the letters to spell "FLIK" to gain a bonus life. Repeat this to obtain as many lives as needed before resuming the regular game.
When the level description appears at the start of a level, hold Z + R + L. Note: The invincibility only lasts for the current level.
Easier Level Select
Go to the anthill main menu and just press c-up and R at the same time and hold it for three seconds and all the levels will be unlocked.