Rock the Fish

 is a trophy item. The method of obtaining is from the Dark monolith with a chance assumed to be around 1% (This is unconfirmed.)

It is likely that the chances are much lower than 1% due to the small amount of rock the fish's in existence, and tests by the community.

Some people assume that the chance is 0.01% to 0.2%, again, this is unconfirmed.