A gun that only shoots in one direction might be physically improbable, but it can also turn any platformer that involves shooting into a puzzle game. That's what's happened to MonoDi, in which you puzzle, shoot and jump your way through 25 unexpectedly varied single-screen levels, each sporting functional if cute graphics, lots of alien eggs to destroy, and bits of badly spelled plot to read through.
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The game requires a masterful mix of puzzle solving, pattern recognition and timing as you avoid traps, destroy enemies and tiles, push buttons and - most intriguingly - change the direction in which your gun fires or manage to use it to your advantage.
Said direction can only be altered by going through the game's solar wind streams - handy lightbeams that can be found in most levels and which will help you discover that shooting down will propel you upwards. The mechanic makes for some interesting boss battles too as, during the first one for example, you race to change your direction of fire according to where the baddie has camped.
Beat this boss and you'll get to the meat of the game: MonoDi's brilliant second and third sectors with pure puzzle levels in outer space, new enemies to kill, more weapons, different kinds of eggs to destroy and the aptly named Cube Gun.