More photos would be helpful, I've never heard of a goldfish with one telescope eye? Could it be the illness 'pop eye'?
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As for sticking his head into the others bum, that sounds much like breeding behaviour
From what I understand the males will harass the females to drop their eggs
Also, single tailed goldfish, like your shubunkin, will do better in a pond than in a tank with fancy goldfish. How big is it at the moment? Usually it's safe to upgrade them once they're 6 inches. I currently have a common goldfish that I'm looking after until it's big enough to be moved
Not sure if I'll have a pond myself or if I'll re-home her elsewhere. The reason for ponds is because they grow much bigger than fancies (up to and sometimes over 1 foot in length) and they are much more active than fancies as well, they need lots of space for exercise