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Cross a tower-defense game with the Bejeweled-style gem craze, and you get Crystallight Defense. If you like tower-defense games, this twist adds fun, and increases the difficulty.
The game comes complete with a back-story about a mechanical lord whose iron monsters are invading the human castle from the underground forge. In my opinion, it reads like fantasy science fiction written under the influence of Four Loko, but don't let that deter you from the cool puzzles.
Like a typical tower-defense game, you must pick a puzzle – a track with a beginning and an end, with various twists and turns. Then, you need to place a tower along the edge so you can destroy the invading robots. The twist comes because, in this game, the tower is empty. In order to power it up, you must first mix a crystal from the crystals palette, one of several different colors and powers, to drop into the tower. Mixing the crystals power, fire, acid and ice creates new gems of combined effect. You learn by mixing the best strategy of tower placement and gems.
If things get confusing, the game provides an easy help system. Just press the trackball or D-pad of your phone, then tap on any object in the game; a pop-up explains what it is and how to use it.
You can play for a good while with the free demo. The full version, with more levels, costs $2.95. Check it out.