...The Drunken Bot: looks like player, but it`s green and it smiles to you. Walks in random direction, the same way like player.
A turret: shots in random direction with a constant interval. Bullets can fly through the walls.
The Boss: randomly moves left or right at the top of level, fires from two guns. Starts raging, when his health becomes low.
There are no savegames between levels, so if you`ll lost all backups and die somewhere at 15th level (for example), you will be returned to the first level. At the game's begin you have five backups; collecting of a big green square will give you one more backup (aka 1-UP).