Never heard any mod with X-COM theme before
Spritework aside, I'm not sure if X-COM mod should focus on battle only or should include other elements original game has
Think just for battle scenes.
But with developing the battle units.
Battle 1: Just a scout UFO with one alien
Battle 2: Exploration UFO
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Locate Enemy Bases
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Anhilate renegade governments
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PSI Battels
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Terror Missions
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Learn about the Marsian origin
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Battle on Mars