Dunno how rare it is, but my favorite piece in my vinyl collection is my Metallica CREEPING DEATH 1-inch 45 RPM picture disc. I also have a "combo" vinyl with the CREEPING DEATH EP on one side and the JUMP IN THE FIRE EP on the other.
I've got a couple of other weird things, again, dunno how rare they are, but I like'em ... Twisted Sister's UNDER THE BLADE (Secret Records pressing), The MEAN MAN and 9.5-N.A.S.T.Y. 12 inch singles from W.A.S.P. (with non-album tracks on the B-side), Lillian Axe's LOVE AND WAR, and a few others I can't think of off the top of my head. The vinyl collection is in a crate in the closet and doesn't get pulled out much anymore...
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"If you're a false, don't entry, because you'll be burned and died!"