Robocop

First of all, on the first level there is a building that houses five objects. Collect them in this order -

The Cake,
The Hammer,
The Earth / Globe,
The Apple (the sort of gold coloured object)
The Tap

Once they have been collected in that order, you will be invincible!

Pause the game and type BEST KEPT SECRET for invincibility.

Pause game play, then hold [Shift] and type alex murphy. Hold The Left Mouse Button to regain energy.