The Linux version of Overgrowth has different dependencies which need to be fulfilled otherwise the game won't run. Those dependencies can vary from distribution to distribution, so it would be a good thing to write them down.
Overgrowth needs different libraries in order to work. This list might be not complete.
emerge -av media-libs/freeimage emerge -av media-libs/freealut emerge -av media-libs/libpng:1.2
If your user is not already in this groups you have to add him. Otherwise the game may not start and it is even possible that X will completely crash.
gpasswd -a your_user audio gpasswd -a your_user video
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