Complete all the three stages of all 4 world with 100 fireflies in every stage and you will get a bonous stage in every world.If you complete the bonous stage also with 100 fireflies then you will get a cheat opened.
Note:
To get the cheats enabled go to [Main Menu-->Options-->Cheats and Extras]
If you need more help, we've got more Zapper cheats and also check out all of the answers for this game
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