The original only had one mode, but I have added:

Easy mode:

• Start with 5 lives instead of 3.
• Enemies/bosses have lower health.
• Your score and bonuses will be reduced

Hard mode:

• Start with 3 lives as normal.
• Enemies/bosses will have more health.
• Your score and bonuses will be increased.

Challenge mode:

• Start with 3 lives
• No extra lives will appear in the game (they are replaced with health power ups)
• Plays like normal difficulty and normal scores apply.

Trainer mode:

• Plays like normal difficulty and normal scores apply.
• No score is recorded in the hiscore table.
• Can enable infinite lives, health, powerlines, etc. from the menu.
• Use the following cheat keys:
• F1: Restore Health
• F2: Extra Life
• F3: Shield
• F5: Skip Level
• F6: Skip World
• 1/2: Adjust multiple weapon strength
• 3/4: Adjust laser weapon strength
• 5/6: Adjust bounce weapon strength
• 7/8: Adjust lightning length
• 0: Smart bomb