Unknown File Format

[cdkiller]

I've been exploring around with a game I have that contains a file/archive with the .arc extension

if it´s a game its most likely a custom archive coded by the game developers.
the file extension name doesn´t always mean it´s an archive where an extractor is available.
you could open it with a hexeditor an check the header for some known strings like "RAR!" or "PKZip" etc...