Originally thought of doing Real-time Strategy Settled on Tower Defense subgenre instead (less content creation required)

It supports co-operative play Controller based rather than keyboard/mouse based

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Built level editor tool to ease mapping of tiles to background image

Level editor in action Level 3 Background Image Level 3 Having Tiles Mapped In Level Editor

Audacity used to edit, clean up and add effects sounds

Under Creative Commons License (most effects from here)