CrabEvo: You pick a crab, you make a small modification to it, and upload it. Ideally you have a narrative, tell a story about how your crab endures against the environment and other crabs. Is this an arms race or a story of symbiosis? Evolving your own crab? This is fine. Evolving other people's crab? Also fine. A species is not extinct unless I say so, they just fade into the background.

Setting: The small island is home to a simple collection of soft shelled crab like creatures. A bubbling, steaming, muddy plain in the center is warm at night, but a bit too hot during the day to be comfortable. From the bubbling mud comes precious nutrients. The terrain of mud gives way to a brackish delta all around the island, in turn giving way to expansive shallows of salt and silt.

A crab can live here comfortably, but without advancement, it will never thrive, it will never amount to anything.